Tolcap Glossary

σ, Standard Deviation: (Greek letter, small sigma) A statistical measure of the variation within a set of data values.
6σ, Six Sigma: A statistical technique for refining manufacturing processes. Six Sigma targets fewer than 3.4 defective parts per million produced.
Related: Design for Six Sigma
ABS, acrylonitrile butadiene styrene (thermoplastic): A tough, impact resistant thermoplastic. A polymer comprised of three monomers. With a glass transition temperature ≈105°C ABS is useful for parts functioning in the range −20 to 80°C. ABS has good water, acid/alkali and oil resistance.
Lego bricks and the faceplates of wall sockets are familiar forms of ABS. Use Tolcap to work out process capable tolerances for dimensions on parts involving extrusion, blow moulding, rotational moulding, precision injection moulding or injection compression of ABS.
Additive Manufacturing Technology: Material is added together to create parts by e.g. 3D printing.
Related Subtractive and Formative.
anisotropic: Describes an object or material whose physical properties have different value when measured in different directions
e.g. plastics with aligned polymer chains may stretch more readily if the force acts in the same direction as chains lie, wood is stronger along the grain than across it.
ANSI B4.1 Standard, also known as ASME B4.1 Standard: Preferred Limits and Fits for Cylindrical Parts
An American National Standards Institute / American Society of Mechanical Engineers standard relating to running, sliding and interference fits.
ANSI B4.2 Standard, also known as ASME B4.2 Standard: Preferred Metric Limits and Fits
A metric version of ANSI/ASME B4.1. Use Tolcap to help you achieve the standards recommended.
APQP, Advanced Product Quality Planning: A quality management system for developing new products. Widely used in the automotive industry but applicable to any industry. Similarities to DFSS.
ASME Y14.5-2009 Standard: Dimensioning and Tolerancing
An 2009 American Society of Mechanical Engineers standard that describes how to set out geometric tolerances and explains what they mean. In this interesting video GD&T experts from Tec-Ease talk about the changes introduced by the ASME Y14.5-2009 Standard.
Axial / Radial: The diagram below illustrates axial and radial distances in Cold Heading.
Blanking ( Manufacturing Process ): A manufacturing process in which shapes are punched through a sheet of metal. The piece of material that is removed forms the required workpiece, referred to as a blank. The blank may then be subject to further processing.
See also Fine blanking .
Materials: metals and alloy sheet
Typical applications: thin flat metal objects, spacers, washers
Blow Moulding ( Manufacturing Process ^{Ref 1} ): A hot plastic tube is inflated inside a mould. The workpiece is allowed to cool and the mould split to eject the component.
Materials: thermoplastics
Typical applications: hollow plastic objects with thin walls, bottles, ducting Tolcap can be used to find process capable tolerances for blow moulded thermoplastics with dimensions 10 to 500mm.
Broaching ( Manufacturing Process ^{Ref 1} ): A machining process which removes unwanted metal from a component by chipping away with a toothed tool pulled or pushed across the surface.
Materials: metals and alloys
Typical applications: connecting rods, gear teeth, drive shaft splines Tolcap can be used to find process capable tolerances for broached: steel alloy, cast steel, free cut steel, medium & high carbon steel, mild steel, stainless steel, tool steel; aluminium, copper, lead, magnesium, nickel, tin, titanium, and zinc alloys; and grey iron; with dimensions 1 to 150mm.
BS 8888:2017 Standard: Technical product documentation and specification
This British Standard for engineering drawings and geometrical tolerancing describes how to set out geometric tolerances and explains what they mean. Tolcap's Richard Batchelor gives a brief overview of Tolerance related standards in his Sept 2017 Blog
BS 308 Standard: British Standard superseded by BS 8888.
BS EN 20286 Standard: ISO system of limits and fits. ISO system of limits and fits. Bases of tolerances, deviations and fits
The British Standard equivalent of ISO 286. Use Tolcap to help you achieve the standards recommended.
BS EN ISO 2692 Standard: Geometrical product specifications (GPS). Geometrical tolerancing. Maximum material requirement (MMR), least material requirement (LMR) and reciprocity requirement (RPR).
This British Standard for engineering drawings and geometrical tolerancing describes how to set out geometric tolerances and explains what they mean. It also treats Geometrical Product Specifications - how dimensions on drawings must show the proper relationships and alignment of features.
Bushing ( Manufacturing Process ): A temporary cylindrical lining used as a tool guide, and/or to size or protect an opening during manufacturing.
CA, cellulose acetate (thermoplastic): An early synthetic thermoplastic fibre created from wood pulp or cotton. CA materials wick and drys quickly, they drape and dye well, but the fibres are weak and the materials produced are not very durable. Use Tolcap to work out process capable tolerances for dimensions on parts involving extrusion, blow moulding, rotational moulding, precision injection moulding or injection compression of CA.
CAD, Computer Aided Design: Any use of computers during the process of design.
Common CAD software enables the designer to create 2D drawing or 3D models that may detail dimensions, tolerances, materials and processes to be employed.
CAE, Computer Aided Engineering: Engineering use of computer software typically to help in design, simulations, and optimisation.
Capable: See Process Capable
See also: C_pk to ppm correlation Process Capability, Capability, Cp, C_pk Process Capability Index / Indices, Cp, C_pk Process Capability Map Process Capable Tolerancing
Capability: See Process Capability
See also: C_pk to ppm correlation Process Capable, Capable Process Capability Index / Indices, Cp, C_pk Process Capability Map Process Capable Tolerancing
Capability Analysis: A statistical determination of the ability of a manufacturing process to meet design specifications.
Capability Map: See Process Capability Map
Casting ( Manufacturing Process ): Liquid material is poured into a cavity of the required shape in a mould. The liquid is allowed to solidify and the component is removed or broken out of the mould.
Materials: metals, clay, concrete, epoxy, plaster, plastics
Typical applications: can be used to create intricate shapes e.g. pulley wheels, gears, ornaments Tolcap can be used to find process capable tolerances for a wide range of casting types:

Centrifugal Casting - all metals

Ceramic Mould Casting - all metals

Gravity Die Casting for aluminium, copper, iron and magnesium alloys

Investment Casting - all metals

Plaster Mould Casting for aluminium, copper, magnesium and zinc alloys

Pressure Die Casting for aluminium, copper, magnesium and zinc alloys

Sand Casting for aluminium, copper and magnesium alloys, iron and steel

Shell Moulding for aluminium, copper, iron, magnesium and steel alloys
CAQ, Computer Aided Quality Assurance: The use of computer controlled machinery, and computer applications, to enhance the quality of product specification and to inspect product quality. Tolcap is a CAQ application.
Centrifugal Casting ( Manufacturing Process ^{Ref 1} ): Molten material is poured into, and coats the walls, of a hollow rotating mould.
Materials: most metals, glass, plastics, ceramics, concrete
Typical applications: hollow cylinders e.g. pipes, gun barrels, pulley wheels, gears Tolcap can be used to find process capable tolerances for centrifugally cast metals of dimensions 10 to 1500mm.
Ceramic Mould Casting ( Manufacturing Process ^{Ref 1} ): A metal pattern is coated in a ceramic slurry which is dried and baked to create a mould. Molten metal is poured into the mould and left to solidify. The part is removed by breaking the mould.
Materials: metals - typically stainless steel and bronze
Typical applications: creating moulds for other casting and forming processes, cutting tool bodies, industrial tools Tolcap can be used to find process capable tolerances for ceramic mould cast metals of dimensions 1 to 1000mm.
Characteristic Dimension: The important dimension that defines the size of the feature of a part that is currently under consideration.
Related: Critical Characteristic , Critical-To-Quality , Key Characteristic
Chemical Machining, CM ( Manufacturing Process ^{Ref 1} ): A workpiece is masked with tapes, paints or plastics then immersed in a solution (usually acid or alkali) that etches away unmasked areas.
Materials: metals, alloys, silicon
Typical applications: weight reduction for aerospace components, circuit boards, cavity creation Tolcap can be used to find process capable tolerances for chemically milled aluminium alloys, carbon steels and titanium with dimensions 1 to 15mm.
Closed Die Manufacturing Techniques: Closed die manufacturing processes deform material within dies that fully enclose and shape the material.

Related: Open Die
Computer Numerical Control Machining, CNC Machining ( Manufacturing Technology ): Accurate computer aided manufacture using subtractive tools such as lathes, grinders, mills and routers. Tools derive instruction directly from a CAD file.
Requires little human intervention, consequently often cost effective. High accuracy achievable.
Cold Drawing ( Manufacturing Process ): Metal is drawn or pulled at room / low temperature through a die stretching it to the desired shape and thickness.
Materials: metals which are ductile at low temperatures
Typical applications: wires, bars, tubes

Related: Cold Forming. Tolcap can be used to find process capable tolerances for cold drawn copper and copper alloys of dimensions 1 to 100mm, and low to medium carbon steels of dimensions 1 to 150mm.
Cold Forming ( Manufacturing Process ^{Ref 1} ): Metals are pressed, extruded / impacted, drawn, swaged, headed or rolled into the desired shapes at room or low temperature.
Materials: metals which are ductile or malleable at low temperatures
Typical applications: fasteners, gear blanks Tolcap can be used to find process capable radial tolerances for cold formed aluminium, copper, lead, magnesium, nickel, steel, tin and zinc alloys, and medium carbon, high carbon, stainless and mild steel of dimensions 1 to 100mm. ( See also the linked processes. )
Cold Heading ( Manufacturing Process ^{Ref 1} ): The metal component is held in a die with a section protruding. The protrusion is struck with punches deforming it to the punch shape.
The size of the component across the die - radially - is determined largely by the dimensions of the die (/ punch) with which it is pressed into contact. Variations in the mass of the component will influence the axial length of the resultant part, and axial variation is usually greater than radial variation.
Materials: metals which are ductile at low temperatures
Typical applications: nails, screws, electronic components

Related: Cold Forming. Tolcap can be used to find process capable tolerances for cold headed low and medium carbon steel of axial dimensions 1 to 300mm and radial dimensions 1 to 30mm.
Cold Rolling ( Manufacturing Process ): Metal sheets are drawn through rollers at room / low temperature.
Materials: metals which are ductile at low temperatures
Typical applications: metal sheets, strips, bars

Related: Cold Forming. Tolcap can be used to find process capable tolerances for cold rolled aluminium, copper, copper alloys, and low and medium carbon steel of dimensions 0.1 to 100mm.
Compression Moulding ( Manufacturing Process ^{Ref 1} ): Unpolymerized plastic is placed in a heated mould. The mould is closed under pressure squeezing the heat melted plastic into all mould areas.

Materials: most commonly thermoset plastics, also composites, elastomers and thermoplastics
Typical applications: handles, lids, electrical components Tolcap can be used to find process capable tolerances for compression moulded composite materials of dimensions 10 to 3000mm.
Contact Moulding ( Manufacturing Process ): Also known as Hand-spray lay-up.
Control Charts, Shewhart Charts: A statistical manufacturing process control tool.
The graph to the right shows a control chart: A plot of how process data changed over time: The central (green) line indicates the data average,
the top (red) line is the upper control limit
and the bottom (blue) line is the lower control limit.
Average, upper and lower limits are determined from previous data.
Cost v Tolerance: Manufacturing tighter tolerances requires: more sophisticated machinery; more precise moulds and dies; more time consuming and skilled operations - hence manufacturing a smaller tolerance is more costly than manufacturing at large tolerance.
Relevant Tolcap articles:

Counting the Cost of Quality

Process Capable Tolerancing
C_p: See Process Capability Indices (centred, typically unrealistic)
See also: C_pk to ppm correlation Process Capable, Capable Process Capability, Capability, Cp, C_pk Process Capability Index / Indices, Cp, C_pk Process Capability Map Process Capable Tolerancing
CP, cellulose propionate (thermoplastic): Stronger, lighter and more flexible than cellulose acetate, CP is a particularly transparent and glossy thermoplastic. CP is familiar in cutlery and tool handles, spectacle frames and googles. Use Tolcap to work out process capable tolerances for dimensions on parts involving extrusion, blow moulding, rotational moulding, precision injection moulding or injection compression of CP.
C_pk: See Process Capability Indices (real world adjusted)
See also: C_pk to ppm correlation Process Capable, Capable Process Capability, Capability, Cp, C_pk Process Capability Index / Indices, Cp, C_pk Process Capability Map Process Capable Tolerancing
Critical Characteristic (CC): A Critical Characteristic is a feature of a material, process, or part (including assemblies) that, if missing or not conforming to the design data, quality requirements, or overhaul and maintenance documentation, would result in an unsafe condition, and/or a non-compliance with a regulatory requirement (legal or environmental).
Related: Key Characteristic , Significant Characteristic
CSSBB, Certified Six Sigma Black Belt: See Six Sigma Black Belt
CTQ, Critical-To-Quality: Critical product characteristics whose specification must be met if customer requirements are to be supplied.
Related: Critical Characteristic, , Characteristic Dimension , Key Characteristic
Cylindrical Grinding ( Manufacturing Process ^{Ref 1} ): A machining process which removes unwanted material from a rotating component by an outer abrasive wheel.
Materials: hard inflexible materials
Typical applications: parts requiring smooth surfaces and close tolerances, gears, cams Tolcap can be used to find process capable tolerances for cylindrically ground: steel alloy, cast steel, free cut steel, medium & high carbon steel, mild steel, stainless steel, tool steel; nickel, and titanium alloys; and grey, malleable, modular, and pearlite iron; with dimensions 1 to 1000mm.
Deep Drawing, Cup Drawing ( Manufacturing Process ^{Ref 1} ): A manufacturing process in which a metal sheet is deformed by a punch forcing the sheet into a die cavity.
The draw is consider 'deep' if the depth of the deformation exceeds its diameter.

Materials: metals and alloys
Typical applications: cup shaped objects, cans, kitchen sinks Tolcap can be used to find process capable tolerances for deep drawn: steel alloy, medium & high carbon steel, mild steel, stainless steel; aluminium, copper, lead, magnesium, nickel, tin, titanium, and zinc alloys with dimensions 1 to 500mm.
Design for Assembly, DFA: A methodology for designing products with ease of assembly in mind e.g. by reducing the number of components or creating easily gripped features.
Design for Manufacture, Design for Manufacturing, Design for Manufacturability, DFM: The practice of creating product designs that simplify manufacture.
Design for Manufacture and Assembly, DFMA: Combines DFA and DFM.
Design for Six Sigma, DFSS: Manufacturing design that employs Six Sigma techniques from the outset. This aims to produce less than 3.4 defective parts per million by early consideration of, and allowance for, potential manufacturing process and material issues.
DFMEA, Design FMEA, Design Failure Mode & Effect Analysis: FMEA aiming to uncover design failings effecting product safety, usability, and durability.
Die ( Manufacturing Tool ): A tool used to cut, shape, bend, or finish a manufactured part.
DIN 16742 Standard: Plastics Moulded Parts - Tolerances and Acceptance Conditions
Deutsches Institut für Normung e.V. standard related to tolerancing plastic components - particularly injection mouldings. In his Rough Guide to Tolerancing Plastic Mouldings blogs series Tolcap guru Richard Batchelor discusses the relationship between Tolcap and the Standard's guidance to plastics tolerancing.
DIN 1688-4 Standard: Light metal alloy raw castings; pressure die castings; general tolerances, machining allowances
Deutsches Institut für Normung e.V. standard. Now WITHDRAWN.
DIN 16901 Standard: Plastic mouldings - Tolerances and acceptance conditions for linear dimensions
Deutsches Institut für Normung e.V.
Editions published in July 1973, November 1982
Standard superseded by DIN 16742. In his Rough Guide to Tolerancing Plastic Mouldings - Tolcap or DIN 16901? blog Tolcap guru Richard Batchelor discusses the relationship between Tolcap and the DIN 16901 standard.
DMAIC, Define Measure Analyze Improve & Control: A data driven Six Sigma quality improving cycle:

Define process, limitations and expectations

Measure results

Analyse measured data collected against defined expectation

Improve inadequacies detected in analysis

Control the process via monitoring and documentation
DPMO, Defects Per Million Opportunities: $DPMO = \frac{Total number of defects in the sample x 1,000,000}{Number of units in the sample x Number of opportunities for a defect per unit}$
$= DPO x 1,000,000$ DPMO = ( Total number of defects in the sample x 1,000,000 ) / ( Number of units in the sample x Number of opportunities for a defect per unit )
= DPO x 1,000,000
e.g. In a sample of 50 simple cylindrical metal units each unit is judged to have 5 opportunities for defect (length, width, straightness, smoothness, hardness).
10 units are found to have 1 defect, 6 have 2 defects, 1 has 3 defects:
$\frac{(10 + 6 x 2 + 3) x 1,000,000}{50 x 5} = \frac{25 x 1,000,000}{50 x 5} = 100,000$ 1,000,000( 10 + 6x2 + 3 ) / ( 50 x 5 )
= 25,000,000 / ( 50 x 5 ) = 100,000 defects per million opportunities

DPO is commonly used in Six Sigma Metrics.

See also PPM.
DPO, Defects Per Opportunity: $DPO = \frac{Total number of defects in the sample}{Number of units in the sample x Number of opportunities for a defect per unit}$
$= \frac{DPU}{Number of opportunities for a defect per unit}$ DPO = Total number of defects in the sample / ( Number of units in the sample x Number of opportunities for a defect per unit )
= DPU / Number of opportunities for a defect per unit
e.g. In a sample of 50 simple cylindrical metal units each unit is judged to have 5 opportunities for defect (length, width, straightness, smoothness, hardness).
10 units are found to have 1 defect, 6 have 2 defects, 1 has 3 defects:
$\frac{10 + 6 x 2 + 3}{50 x 5} = \frac{25}{50 x 5} = 0.1$ ( 10 + 6x2 + 3 ) / ( 50 x 5 ) = 25 / ( 50 x 5 ) = 0.1 defects per opportunity

DPO is commonly used in Six Sigma Metrics.
DPU, Defects Per Unit: $DPU = \frac{Total number of defects in the sample}{Number of units in the sample}$ DPU = Total number of defects in the sample / Number of units in the sample
e.g. In a sample of 50 units, 10 have 1 defect, 6 have 2 defects, 1 has 3 defects:
$\frac{10 + 6 x 2 + 3}{50} = \frac{25}{50} = 0.5$ ( 10 + 6x2 + 3 ) / 50 = 25 / 50 = 0.5 defects per unit

DPU is commonly used in Six Sigma Metrics.
Drilling ( Manufacturing Process ^{Ref 1} ): A machining process which chips away unwanted material using a rotating tool with cutting edges to create a cylindrical hole in the component.
Materials: metals, alloys, some plastics and ceramics
Typical applications: parts requiring cylindrical holes Tolcap can be used to find process capable tolerances for drilled: steel alloy, cast steel, free cut steel, medium & high carbon steel, mild steel, stainless steel, tool steel; aluminium, copper, lead, magnesium, nickel, tin, titanium, and zinc alloys; and grey iron; with dimensions 1 to 100mm.
EBM, Electron Beam Machining ( Manufacturing Process ^{Ref 1} ): A narrow beam of high energy electrons create areas of intense heat vaporizing the workpiece material.
Materials: all materials
Typical applications: accurate cutting or boring, engraving, silicon wafers Tolcap can help you establish suitable process capable tolerances for Electron Beam Machined dimensions from 1 to 100mm.
ECM, Electrochemical Machining ( Manufacturing Process ^{Ref 1} ): ECM is a method of removing material by passing a high electric current between an electrode and the processed part through a conductive fluid.
Materials: electrical conductors, typically used for extremely hard metals, some ceramics
Typical applications: intricate shapes and fine mirror finishes Tolcap can help you establish suitable process capable tolerances for Electrochemically Machined dimensions from 1 to 100mm.
EDM, Electrical Discharge Machining, Spark Machining, Spark Eroding, Burning, Die-Sinking, Wire Burning, Wire Erosion ( Manufacturing Process ^{Ref 1} ): Pulsed electrical discharges between an electrode and the workpiece generate heat (and sparks) which precisely melt and remove material.
Materials: electrical conductors, typically used for tool steels and copper alloys
Typical applications: prototype parts, burr free parts, irregular structures Tolcap can help you establish suitable process capable tolerances for Electrical Discharge Machined parts of dimensions 1 to 100mm.
Elastomer: Solid polymers with rubber like elasticity.
Typical applications: seals, shoe soles, tyres, tubes
Related: Plastic. Use Tolcap to work out process capable tolerances for 1 to 150mm dimensions on parts involving injection moulding of elastomers.
Epoxy, Polyepoxides (thermoset): A range of strong thermoset polymers with high temperature tolerance and chemical resistance.
A good electrical insulator but with good heat conduction epoxy is used in circuit boards. With high strength and low weight epoxy is popular for marine and aerospace applications. Often reinforced with glass or carbon fibres. Use Tolcap to work out suitable process capable tolerances for dimensions on parts involving injection compression of Epoxy.
Extrusion ( Manufacturing Process ): A material is pushed through a die of the required shape creating a regular cross section on the component.
Extrusion can be performed cold or hot depending on the material being extruded.
Materials: metals, plastics, clay, concrete
Typical applications: rods, bars, tracks Tolcap can be used to find process capable tolerances for cold extruded medium & high carbon steel, mild steel, stainless steel, and aluminium, copper, lead, magnesium, nickel, steel, tin and zinc alloys with dimensions 1 to 150mm.
It can be used to find process capable tolerances for hot extruded aluminium and magnesium alloys with dimensions 1 to 300mm.
For extruded elastomers Tolcap calculates process capable tolerances for characteristic dimension 1 to 100mm.
For extruded thermoplastics Tolcap calculates process capable tolerances for characteristic dimension 1 to 500mm.
Filled / Unfilled polymer: Small quantities of solids such as carbon black, silica, talc; or liquids such as oils or plasticizers; are added to ‘unfilled’ polymer creating ‘filled’ polymer. The addition of filler materials improves the physical properties; or aids the processing; of the polymer. Tolcap can be used to find process capable tolerances for injection compressed: filled and unfilled PBTP; filled PETP; filled POM; filled and unfilled PP.
Fine Blanking ( Manufacturing Process ): Fine blanking is a particularly controlled blanking process. The sheet metal is held taut to prevent deformation and achieve superior flatness in the blanks produced.
Materials: metals and alloy sheet
Typical applications: thin flat metal objects, spacers, washers Tolcap can be used to find process capable tolerances for fine blanked: steel alloy, medium & high carbon steel, mild steel, stainless steel; aluminium, copper, lead, magnesium, nickel, tin, titanium, and zinc alloys with dimensions 1 to 500mm.
Fixture: A fixture is a work holding device, which holds, supports and locates the workpiece but does not guide the cutting tool to perform a specific operation.
If it guides a tool it is a Jig.
Flash, Flashing, Flashes: Material that has seeped at mould or die parting lines.
For the user input manufacturing process, material and dimension, Tolcap calculates tolerance and process capability. If process appropriate Tolcap allows the user to take into account parting line issues such as flashing.
FMEA, Failure Mode & Effect Analysis: A highly structured technique for finding potential failures in a design, manufacturing process or product.
FMECA, Failure Mode Effect & Criticality Analysis: See FMEA, but FMECA goes into more detail, ranking those errors with the highest criticality (charts the probability of failure modes against the impact of the consequences) bringing focus on the most critical aspects.
Formative Manufacturing Technology: Parts are created by reshaping or deforming material to the required shape, without removing or adding material e.g. casting and moulding.
Related Subtractive and Additive.
GD&T, GDT, Geometric Dimensioning and Tolerancing: Symbols used on mechanical engineering drawings to specify the acceptable range of dimensions. Tec-Ease website maintain a good list of GD&T symbols.
Gravity Die Casting, Permanent Mould Casting ( Manufacturing Process ^{Ref 1} ): Molten metal is poured under gravity into a die where it solidifies. The die is opened to remove the casting.
Materials: metals - most commonly copper, aluminium and magnesium
Typical applications: connecting rods, pistons, gear and die blanks Tolcap can be used to find process capable tolerances for gravity die cast aluminium, copper, iron and magnesium alloys of dimensions 1 to 1000mm.
Hard materials: Hard materials resist plastic deformation.
Hand-spray lay-up, Contact moulding ( Manufacturing Process ): Polymer resin and fibrous reinforcer are sprayed by hand on to a shaped mould (either simultaneously or one after the other). The material is cured either at room, or a raised, temperature. After curing the part can be removed from the mould.
Materials: epoxy, polyester, polyvinyl ester, PF, UP, polyurethane resin. Typical reinforcers include glass, carbon or natural plant fibres.
Typical applications: tubs, boats, automotive parts Tolcap can be used to find process capable tolerances for hand-spray lay-up composite materials of dimensions 10 to 5000mm.
HDPE, High-density polyethylene, PEHD, Polyethylene high-density (thermoplastic): A rigid, transparent, often low cost thermoplastic. Used in producing a plastic bottles, pipes and environmental membranes.

Related: plastic, thermoplastic.
Honing ( Manufacturing Process ^{Ref 1} ): A machining process in which an abrasive stone is rubbed over areas of the workpiece to remove small amounts of surface material.
Materials: metals, alloys, some ceramics and plastics
Typical applications: rifle bores, engine cylider bores, dowel holes Tolcap can be used to find process capable tolerances for honed: steel alloy, cast steel, free cut steel, medium & high carbon steel, mild steel, stainless steel, tool steel; nickel, and titanium alloys; and grey, malleable, modular, and pearlite iron; with dimensions 1 to 500mm.
Hot Forging ( Manufacturing Process ^{Ref 1} ): A heated metal component is shaped by pressure or impact via presses, hammers or dies.
Materials: Metals and alloys
Typical applications: crankshafts, tool bodies, levers Tolcap can be used to find process capable tolerances for closed die hot forged low to & medium carbon steel (up to 50kg), and low alloy steel (also up to 50kg) for dimensions in the range 5 to 1500mm (range dependent on kg).
Tolcap can also be used to find process capable tolerances for precision closed die forged and stamped copper alloys with characteristic dimensions 1 to 300mm.
Impact Extrusion ( Manufacturing Process ): A metal slug is struck by a punch at high velocity pushing it into a die or mold.

Materials: Metals and alloys
Typical applications: fasteners, gear blanks, battery outer tubes

Related: Cold Forming. Tolcap can be used to find process capable axial and radial tolerances for impact extruded medium & high carbon steel, mild steel, stainless steel, and alloys of aluminium, copper, lead, magnesium, nickel, steel, tin and zinc - for dimensions in the range 5 to 150mm.
Injection Moulding ( Manufacturing Process ^{Ref 1} ): Polymer is heated and forced under pressure into a mould cavity.

Materials: most commonly thermoplastics, also composites, elastomers and thermosets
Typical applications: tool handles, containers, electrical parts, complex precise plastic components Tolcap can be used to find process capable tolerances for injection moulded elastomer with dimensions 1 to 150mm, and injection moulded thermoplastics with dimensions 1 to 500mm. In his Rough Guide to Tolerancing Plastic Mouldings blogs series Tolcap guru Richard Batchelor discusses the relationship between Tolcap and the Standard's guidance to plastics tolerancing.
Injection Compression ( Manufacturing Process ): A hot plastic is injected into a partly open split mould. The mould halves are compressed together forcing the plastic into the mould shape. The workpiece is allowed to cool and the mould split to eject the component.
Materials: thermoplastics, thermosets
Typical applications: seals, piston rings, pump parts
Tolcap can be used to find process capable tolerances for injection compressed: ABS, CA, CP, Epoxy, PA, PBTP (filled & unfilled), PC, PCTFE PE, PESU, PETP (filled), PF, PMMA, POM (filled), PP (filled & unfilled), PPS, PS, PSU, PVC-U, SAN, UP with dimensions 1 to 1000mm.
Investment Casting ( Manufacturing Process ^{Ref 1} ): A wax pattern is created from a mould. The wax pattern is coated in a ceramic slurry which is cast. The wax pattern is melted out and molten metal poured in. The part is removed by breaking the ceramic mould.

Materials: metals

Typical applications: turbine blades, vehicle engine components, figurines Tolcap can be used to find process capable tolerances for investment cast metal alloys of dimensions 1 to 700mm.
Ironing ( Manufacturing Process ): A manufacturing process in which a deep drawn metal component is forced by a punch through a further restricting die that thins the wall thickness of the component. Typically the thickness is reduced by approximately 50%.
Materials: metals and alloys
Typical applications: cup shaped objects, drinks cans Tolcap can be used to find process capable tolerances for deep drawn and ironed: steel alloy, medium & high carbon steel, mild steel, stainless steel; aluminium, copper, lead, magnesium, nickel, tin, titanium, and zinc alloys with dimensions 1 to 500mm.
ISO 14405 Standard: Geometrical product specifications (GPS) - Dimensional tolerancing -
Part 1: Linear sizes
Part 2: Dimensions other than linear sizes
This standard from the International Organization for Standardization treats Geometrical Product Specifications. This is about how dimensions on drawings must show the proper relationships and alignment of features.
ISO 1829 Standard: Produced by the International Organization for Standardization now superseded by ISO 286.
ISO 20457:2018 Standard: Plastics moulded parts — Tolerances and acceptance conditions
This 2018 standard from the International Organization for Standardization specifies possible manufacturing tolerances for plastic moulded parts. In his Rough Guide to Tolerancing Plastic Mouldings blogs series Tolcap guru Richard Batchelor discusses the relationship between Tolcap and the Standard's guidance to plastics tolerancing.
ISO 2768 Standard: General tolerances —
Part 1: Tolerances for linear and angular dimensions without individual tolerance indications
Part 2: Geometrical tolerances for features without individual tolerance indications
This 2017 reviewed and confirmed standard from the International Organization for Standardization describes how to set out geometric tolerances and explains what they mean.
ISO 286 Standard: Geometrical product specifications (GPS) — ISO code system for tolerances on linear sizes -
Part 1: Basis of tolerances, deviations and fits
Part 2: Tables of standard tolerance classes and limit deviations for holes and shafts
Fits and Limits standards from the International Organization for Standardization. Use Tolcap to help you achieve the standards recommended.
ISO 8062 Standard: Geometrical product specifications (GPS) — Dimensional and geometrical tolerances for moulded parts —
Part 3: General dimensional and geometrical tolerances and machining allowances for castings
Process specific standards for castings (sand through to investment castings) from the International Organization for Standardization. Use Tolcap to help you achieve the standards recommended.
JIT, Just-In-Time Manufacturing, Just-In-Time Production: A methodology developed in Japan. The aim is to reduce stocks of raw materials, work-in-process and finished products by having just the required materials - and no more - arrive where and when needed rather than being available from a stockpile.
Jig: A jig is a work-holding device that holds, supports, and locates the workpiece and guides one or more tools to perform a specific operation.
If it does not guide a tool it is a Fixture.
Key Characteristic (KC): A Key Characteristic is a feature of a material, process, or part (including assemblies) whose variation within the specified tolerance has a significant influence on product fit, performance, service life, and/or manufacturability.
Related: Critical Characteristic , Significant Characteristic
Lapping ( Manufacturing Process ^{Ref 1} ): A manufacturing process in which material is removed from a workpiece by rubbing with abrasive particles.
Materials: all
Typical applications: glass lenses, piston rings, bearing surfaces Tolcap can be used to find process capable tolerances for lapped: steel alloy, cast steel, free cut steel, medium & high carbon steel, mild steel, stainless steel, tool steel; nickel, and titanium alloys; and grey, malleable, modular, and pearlite iron; with dimensions 1 to 500mm.
LBM, Laser Beam Machining ( Manufacturing Process ^{Ref 1} ): Pulsed LASER light is focused on the workpiece vaporizing or liquifying unwanted material.
Materials: all materials
Typical applications: prototype parts, irregular holes, engraving, silicon wafers Tolcap can help you establish suitable process capable tolerances for Laser Beam Machined parts of dimensions 1 to 100mm.
LDPE, Low-density polyethylene, PELD, Polyethylene low-density (thermoplastic): A chemical resistant, often low cost thermoplastic. Used in producing a plastic bottles, bags and tubes.

Related: plastic, thermoplastic.
Lean Production System: See JIT
Lean Manufacturing: A systematic manufacturing methodology that aims to reduce waste in design, manufacturing process, distribution and customer service.
Lean Six Sigma: A combination of Six Sigma and Lean Manufacturing methodologies.
Low-Alloy Steel, High Strength Low Alloy Steel, HSLA, Microalloyed steel: Low-alloy steels are mixtures of low carbon steel with small quantities of - most typically - chrome, nickel and/or molybdenum. They exhibit superior strength and corrosion resistance to simple carbon steels. Tolcap can be used to find process capable tolerances for cold rolled low-alloy carbon steel of dimensions 0.1 to 100mm.
Lower Specification Limit, LSL: See LTL.
Lower Tolerance Limit, LTL: e.g. A rods length specified as 10.0 ± 0.2cm has a LTL 9.8cm.
Machinability: The machinability of a material is a reflection of how easily it can be cut or shaped by a machine.
Machine Capability, Cm, Cmk: Machine Capability is a measure of a machines ability to successfully perform a required production process.
Cmk is calculated using the same formula as those used for C_pk and the standard deviation used for Cmk relates to the single uninterrupted run of the machine.
As with C_pk, a higher value of Cmk reflects greater success i.e. a more successful machine for the required process.
Machining ( Manufacturing Process ^{Ref 1} ): A range of manufacturing processes in which the component shaping involves controlled material removal.
Tolcap can be used to find capable tolerances for a wide range of traditional machining processes for metals and alloys:

Broaching

Cylindrical Grinding

Drilling

Honing

Lapping

Milling

Planing and Shaping

Reaming

Surface Grinding

Turning and Boring
Milling ( Manufacturing Process ^{Ref 1} ): A machining process in which material is chipped from a workpiece using a rotating multiple point cutting tool.
Materials: all metals, some plastics and ceramics
Typical applications: engine blocks, gears, machine components Tolcap can be used to find process capable tolerances for milled: steel alloy, cast steel, free cut steel, medium & high carbon steel, mild steel, stainless steel, tool steel; aluminium, copper, lead, magnesium, nickel, tin, titanium, and zinc alloys; and grey iron; with dimensions 1 to 1000mm.
Moulding: Manufacturing moulding involves putting a melted or liquid material, typically plastics, into a mould and allowing it to set.
Tolcap can be used to find capable tolerances for a range of moulding processes:

Blow Moulding

Compression Moulding

Contact Moulding

Injection Moulding

Rotational Moulding
Near Net Shape, Near-net-shape, NNS (Manufacturing Technique): A manufacturing technique where the initial fabrication produces a part which is close to the intended final shape and size. Such parts require minimal finishing.
Orthogonal axes: Axes that lie at right angles to each other.
Open Die, Free Forging, Smith Forging, Manufacturing Techniques: Open die manufacturing processes deform material by compression between simple dies that do not fully enclose the material.

Related: Closed Die
Overmoulding ( Manufacturing Process ): A two step production process in which an additional layer of material is moulded over the top of an already created part. It can be useful to reduce costs as no manual assembly is required.
Covering materials: plastics, rubber
Typical applications: grips, watertight sealants, attractive or protective finishes
Pareto principle, or 80 / 20 rule: For a large sample, roughly 80% of the outcomes come from 20% of the causes.
PA, polyamide (thermoset): Polyamides such as silk occur naturally. Man made polyamides, such as Nylon, are thermoset polymers. Typically durable and strong. Common uses include textiles, vehicle plastics, food packaging films and carpets. Use Tolcap to find process capable dimensional tolerances for injection compressed polyamide parts.
Parting Line, PL: A line at which sections of casts or moulding dies join. This has the potential to cause a slight step from imperfect mould matching or misalignment, or a ridge due to material seepage ( flash ) at the join.
Often marked as PL on engineering designs.
Parting lines issues are typically found in casting, hot forging and moulding processes. For the user input manufacturing process, material and dimension, Tolcap calculates tolerance and process capability. If process appropriate Tolcap allows the user to take into account parting line issues.
PBTP, PBT, polybutylene terephthalate (thermoplastic): An electrically insulating, impact resisting polyester thermoplastic. PBT has electrical and electronic uses and can be spotted in households as showerheads and toothbrush fibres. Use Tolcap to work out process capable tolerances for dimensions on parts involving extrusion, blow moulding, rotational moulding, precision injection moulding or injection compression (filled and unfilled) of PBT.
PC, polycarbonate (thermoplastic): Easily moulded and thermoformed thermoplastic polycarbonates are typically tough, transparent and heat resistant. Familiar uses include spectacle lenses, DVDs and transparent lightweight greenhouse sheeting. Use Tolcap to work out process capable tolerances for dimensions on parts involving extrusion, blow moulding, rotational moulding, precision injection moulding or injection compression of polycarbonates.
PCTFE, PTFCE, polychlorotrifluoroethylene (thermoplastic): Strong under tension, generally chemical resistant, water proof, transparent. A thermoplastic with a glass transition temperature ≈45°C and heat resistant to 175°C.
Used for transparent films, medical blister packs and water resisting covering for LCD panels. Use Tolcap to find process capable dimensional tolerances for parts involving extrusion, blow moulding, rotational moulding, precision injection moulding or injection compression of PCTFE.
PE, polyethylene (thermoplastic): A very commonly used plastic. Water resistant, largely gas impermeable, impact resisting, a good electrical insulator, it can be made almost transparent. A thermoplastic with melting point between 115–135°C.
Used for packaging, bottles, bags and films. Use Tolcap to work out process capable dimensional tolerances for parts involving extrusion, blow moulding, rotational moulding, precision injection moulding or injection compression of polyethylene.
Permanent Mould Casting ( Manufacturing Process ): Also known as Gravity Die Casting.
PESU, polyethersulphone, polyethersulfone (thermoplastic): A rigid thermoplastic, stable at high temperatures, flame retardant, transparent and chemical resistant. Useful for electrical and electronic parts, and cookware. Use Tolcap to work out process capable tolerances for dimensions on parts involving extrusion, blow moulding, rotational moulding, precision injection moulding or injection compression of PESU.
PET, PETE, polyethylene terephthalate, PET-P (obsolete), PETP (obsolete) (thermoplastic): A common, strong, impact resistant thermoplastic that has good fluid containing properties. Typically spun into clothing fibres or blow moulded into bottles. Use Tolcap to work out suitable process capable tolerances for dimensions on parts involving extrusion, blow moulding, rotational moulding, precision injection moulding or injection compression of PET.
PF, phenol formaldehyde resin, phenolic resin (thermoset & thermoplastic): A class of plastics including the first commercial plastic Bakelite. PF's can be thermoset or thermoplastic depending on production treatments. Commonly used in adhesives for bonding plywood layers and in electrical components. Use Tolcap to find process capable dimensional tolerances for injection compressed PF parts.
Photochemical Blanking, Photochemical Machining, PCM ( Manufacturing Process ): A combination of photochemical resist coating, UV light exposure and corrosive etch allows selected chemical removal of material from the workpiece.
Materials: thin sheets of metals and alloys
Typical applications: circuit boards, prototypes, complex high precision parts Tolcap can help you establish suitable process capable tolerances for photochemically blanked carbon steel and copper alloys parts of dimensions 0.01 to 1mm.
Planing and Shaping ( Manufacturing Process ^{Ref 1} ): A simple machining process in which material is chipped from a straight line on the workpiece by a single point cutting tool.
In planing the tool remains stationary and the workpiece moves.
Shaping involves a stationary workpiece and a moving tool.
Materials: metals and alloys
Typical applications: slots, groves, notches, large gear teeth Tolcap can be used to find process capable tolerances for planed / shaped: steel alloy, cast steel, free cut steel, medium & high carbon steel, mild steel, stainless steel, tool steel; aluminium, copper, lead, magnesium, nickel, tin, titanium, and zinc alloys; and grey iron; with dimensions 10 to 2000mm.
Plaster Mould Casting ( Manufacturing Process ^{Ref 1} ): A metal pattern is coated in a gypsum slurry, the pattern is removed and the plaster is baked. Molten metal poured in and cooled. The part is removed by breaking the mould.
Materials: metals with a low melting temperature (high temperatures damage the plaster mould)
Typical applications: valves, gears, ornaments Tolcap can be used to find process capable tolerances for plaster mould cast aluminium, magnesium, copper, and zinc alloys of dimensions 1 to 500mm.
Plastics: A wide variety of largely synthetic materials formed from long chain polymers usually derived from oil.
Varieties of plastic include: ABS, CA, CP, Epoxy, HDPE (PEHD), LDPE, PA, PBT, PC, PCTFE, PE, PESU, PET (PETE), PF, PMMA, POM, PP, PPS, PS, PSU, PVC-U, SAN, UP.

Related: elastomer, thermoset, thermoplastic. Tolcap can be used to find process capable tolerances for plastics parts formed via extrusion and various forms of moulding (blow moulding, injection moulding, compression moulding, rotational moulding).
PMI, Product and Manufacturing Information: Non geometric details included on a product design that gives information about e.g. dimensional tolerances, materials and finishes. Tolcap is a useful tool to help you specify process capable dimensional tolerances.
PMMA, polymethylmethacrylate (thermoplastic): A rigid, transparent, often low cost thermoplastic. Used in producing a shatterproof alternative to glass for skylights and aircraft glazing. Familiar under tradenames such as Perspex. Use Tolcap to work out process capable tolerances for dimensions on parts involving extrusion, blow moulding, rotational moulding, precision injection moulding or injection compression of PMMA.
POM, polyoxymethylene (thermoplastic): A strong, stiff, hard, opaque thermoplastic. Often injection moulded for high precision components such as small gears wheels, lock mechanisms and ball bearings. Use Tolcap to work out process capable dimensional tolerances on parts involving extrusion, blow moulding, rotational moulding, precision injection moulding or injection compression of POM.
Powder Sintering ( Manufacturing Process ^{Ref 1} ): Compacted powder is subjected to prolonged heating in a mould. The powder fuses creating a workpiece in the shape of the mould.
Materials: typically metals and ceramics
Typical applications: bearings, cutting tools, machine parts Tolcap can be used to find process capable tolerances for powder sintered steel alloy, medium & high carbon steel, mild steel, stainless steel, tool steel; aluminium, copper, nickel, and titanium alloys; and malleable iron; with axial and radial dimensions 1 to 100mm.
Powder Sizing ( Manufacturing Process ): Plastic deformation of sintered parts, typically by forcing the workpiece into a die, to improve dimensional accuracy.
Materials: typically metals and ceramics
Typical applications: bearings, cutting tools, machine parts Tolcap can be used to find process capable tolerances for powder sized steel alloy, medium & high carbon steel, mild steel, stainless steel, tool steel; aluminium, copper, nickel, and titanium alloys; and malleable iron; with radial dimensions 1 to 100mm.
PP, polypropylene (thermoplastic): A heat resistant, tough, translucent, chemical resistant thermoplastic. Used in a wide variety of applications: carpet fibres, crisp packages, kitchen appliances casings and plastic crates. Use Tolcap to work out process capable tolerances for dimensions on parts involving extrusion, blow moulding, rotational moulding, precision injection moulding or injection compression of polypropylene.
PPM, Parts Per Million (Defective): $PPM = \frac{Total number of defective units in the sample x 1,000,000}{Number of units in the sample}$ PPM = ( Total number of defective units in the sample x 1,000,000 ) / Number of units in the sample
e.g. In a sample of 50 units 17 are found to be defective
(in PPM a failed unit is counted only once, even if it has multiple defects, unlike DPMO):
$\frac{17 x 1,000,000}{50} = 340,000$ 1,000,000( 10 + 6 + 1 ) / 50
= 17,000,000 / 50 = 340,000 parts per million defective

PPM is commonly used in Six Sigma Metrics.

See also C_pk to PPM correlation.
PPS, polyphenylene sulfide, polyphenylene sulphide (thermoplastic): A chemical resistant, high temperature tolerating, burn resisting, electrical insulating, opaque thermoplastic. PPS can be moulded, extruded or machined precisely and used in cooking appliances, motor housings and medical equipment. Use Tolcap to work out suitable process capable tolerances for dimensions on parts involving extrusion, blow moulding, rotational moulding, precision injection moulding or injection compression of PPS.
Pressure Die Casting ( Manufacturing Process ^{Ref 1} ): Molten metal is injected into a metal die. It is cooled to solidify and removed by opening the die.
Materials: metals with a low melting temperature (high temperatures reduce the die lifespan)
Typical applications: engine parts, domestic appliances, toys Tolcap can be used to find process capable tolerances for plaster mould cast aluminium, magnesium, copper, and zinc alloys of dimensions 1 to 1000mm.
Process Capable, Capable: The higher the proportion of manufactured dimensions that fall within a design's specified range the more capable the manufacturing process is considered.
See also: C_pk to ppm correlation Process Capability, Capability, Cp, C_pk Process Capability Index / Indices, Cp, C_pk Process Capability Map Process Capable Tolerancing
Process Capable Tolerancing, PCT: A methodology for designing successful components by allocating acceptable dimensional variation taking into account manufacturing process and materials variations.
See also: C_pk to ppm correlation Process Capable, Capable Process Capability, Capability, Cp, C_pk Process Capability Index / Indices, Cp, C_pk Process Capability Map Process Capable Tolerancing
Process Capability, Capability, C_p, C_pk: A number reflecting the success of a manufacturing process.
There are a number of Process Capability Indices with varying reflections of real manufacturing process.

See also: C_pk to ppm correlation Process Capable, Capable Process Capability Index / Indices, Cp, C_pk Process Capability Map Process Capable Tolerancing
For a more comprehensive mathematical consideration of process capability watch our Tolerance Stacks video.
Process Capability (C_pk) to Parts Per Million (ppm) correlation: High process capability indicates low numbers of ppm rejected parts.

Frequently quoted on the internet

Process Capability, C_p Rejected parts per million (ppm)

0.33 317,300

0.67 45,500

1 2,700

1.33 63

1.5

1.67 0.6

2 0.002

Used by TOLCAP

Process Capability, C_pk Rejected parts per million (ppm)

0.33 161,100

0.67 22,200

1 1,350

1.33 33

1.5 3.4

1.67 0.3

2 < 0.1

A plot of ‘Numbers of Manufactured Parts’ versus ‘Part Tolerance’ is typically a standard distribution bell curve. The MEAN is frequently shifted from the TARGET tolerance due to an underlying systematic manufacturing issue: Tolerances may be too small, lying to the left side of the target line, or too large, to the right of the target line.
In the ‘Frequently quoted on the internet’ table (above) the ppm figure reflects the manufactured part being outside tolerance on either side of the TARGET - it includes parts where the tolerance is the too small and where the tolerance is too large.
Tolcap predicts C_pk; C_pk involves measures from the MEAN of the sample to the nearest tolerance LIMIT (in the above graph the LOWER LIMIT). For correspondence to C_pk, Tolcap predicts ppm at the nearer limit i.e. it includes parts where the tolerance is either below the MEAN or above the MEAN, not both. Tolcap's one sided ppm figures, shown in the ‘Used by TOLCAP’ table above, corresponds to roughly half the ppm for the whole distribution. (This is also in keeping with Tolcap's +/- Tolerance format.)
See also: Process Capable, Capable Process Capability, Capability, Cp, C_pk Process Capability Index / Indices, Cp, C_pk Process Capability Map Process Capable Tolerancing

In this blog Richard Batchelor considers Tolcap's C_pk and PPM relationship.

For a more comprehensive mathematical consideration of process capability watch our Tolerance Stacks video.
Process Capability Index / Indices, C_p, C_pk: Process capability can be specified by a number of different indices (they assume normal distribution of a reasonably large sample):
C_p: A comparison of specified output to actual manufactured output.
C_pk: As C_p but takes into account real world variations in manufacturing process, materials and human limitation which result in a non-centred distribution.

C_pk is always less than or equal to C_p
See also: C_pk to ppm correlation Process Capable, Capable Process Capability, Capability, Cp, C_pk Process Capability Map Process Capable Tolerancing

The start of this blog by Richard Batchelor gives a quick explanation of how C_p and C_pk are calculated.
Process Capability Map: Process capability maps can be used to anticipate the number of rejected parts for an intended manufacturing process, material and level of manufacturing accuracy. Or to calculate a suitable manufacturing accuracy based on the required C_pk.

For specific manufacturing processes and materials Tolcap's maps show process capability (Cpk) contours on a graph of tolerance versus dimension.

e.g. for centrifugally cast metals

It is intended to cast a component with dimension of 100mm to a tolerance of ± 0.125mm.
It can be seen from the above plot that (100, 0.125) falls on the 1.33 C_pk contour.
A C_pk of 1.33 corresponds to an expectation of approximately 63 rejected parts per million (ppm).
If the component was cast to a more precise 100 ± 0.075mm the point would fall close to the 0.67 C_pk contour, and the anticipated ppm rejected would increase to around 45500. The shape and location of process capability contours are determined from existing production data and depend on manufacturing process, component material, component geometry, machinery and human factors (Use Tolcap's wizards make allowance for the 3 later factors).
See also: C_pk to ppm correlation Process Capable, Capable Process Capability, Capability, Cp, C_pk Process Capability Index / Indices, Cp, C_pk Process Capable Tolerancing
The data given in Tolcap's maps are representative of good practice in the industry concerned. Data has been collected from a wide range of sources including international standards, specialist organizations, engineering texts and experimental studies. Tolcap maps include as many as twenty different data sources. In all cases the data is consistent with processes that are well established and fully developed.
Process Control: Monitoring and consequent improvement of a manufacturing process.
Process Shift: The tendency of the mean value of a feature produced by a manufacturing process to change with time or batch.
Typical causes of variation: tool wear as the process proceeds; human variation in process set up between one production run and the next.

In this blog Richard Batchelor considers the relationship between process shift and C_pk.
PFMEA, Process FMEA, Process Failure Mode & Effect Analysis: FMEA aiming to uncover process failings effecting product quality, production reliability, worker or environmental safety.
Process Performance, P_pk: A number reflecting the success of a manufacturing process across the entire history of the part.
High process performance indicates low numbers of rejected parts.

This blog by Richard Batchelor gives a quick explanation of how P_pk differs from C_pk.
PPAP, pre-production part approval: A supply chain process used in the automotive industry.
PS, polystyrene (thermoplastic): Inexpensive, transparent, hard, widely used thermoplastic. Typically extruded, moulded and vacuum formed. Familiar as a foamed plastic for packaging and in a solid form as disposable cutlery, yoghurt tubs, lids etc. Use Tolcap to work out process capable tolerances for dimensions on parts involving extrusion, blow moulding, rotational moulding, precision injection moulding or injection compression of polystrene.
PSU, polysulphone, polysulfone (thermoplastic): A tough, rigid, opaque, chemical resistant, thermally stable, but relatively expensive thermoplastic. Typically extruded, injection or blow moulded. Use Tolcap to work out suitable process capable tolerances for dimensions on parts involving extrusion, blow moulding, rotational moulding, precision injection moulding or injection compression of PSU.
PVC-U, unplasticised polyvinylchloride (thermoplastic): Odourless and tasteless PVC-U is ideal for containing food and drinks. A good electrically and thermally insulating, very chemically resistant thermoplastic. Use Tolcap to work out suitable process capable tolerances for dimensions on parts involving extrusion, blow moulding, rotational moulding, precision injection moulding or injection compression of PVC-U.
Radial: See Axial / Radial
Reaming ( Manufacturing Process ^{Ref 1} ): A machining process in which small amounts of material are chipped away to enlarge a hole in a workpiece.
Materials: metals and alloys
Typical applications: cylindrical holes Tolcap can be used to find process capable tolerances for reamed: steel alloy, cast steel, free cut steel, medium & high carbon steel, mild steel, stainless steel, tool steel; aluminium, copper, lead, magnesium, nickel, tin, titanium, and zinc alloys; and grey iron; with dimensions 1 to 100mm.
Right First Time Manufacturing, RFT: A quality management premise suggesting that maximum effort should be expended on design and process before the first manufacturing run. RFT aims to avoid financial and reputational cost from rework and product failure.
Roll Forming ( Manufacturing Process ^{Ref 1} ): A manufacturing process in which sheet metal is gradually bent by passing through a series of progressively tighter rolling dies that incrementally increase the bend.
Materials: metals and alloy sheet
Typical applications: long lengths with constant profiles - light structural supports, tracks, frames Tolcap can be used to find process capable tolerances for roll formed: steel alloy, medium & high carbon steel, mild steel, stainless steel; aluminium, copper, lead, magnesium, nickel, tin, titanium, and zinc alloys with dimensions 10 to 1500mm.
Rotational Moulding ( Manufacturing Process ): Polymer resin is placed in a mould cavity. The cavity is closed, heated and rotated to coat the inside of the mould with melted polymer. The workpiece is then allowed to cool and removed from the mould.
Materials: thermoplastics typically polyethylene, also polypropylene, polyvinylchloride, nylon
Typical applications: seamless, hollow one piece items such as toys, medical equipment, automotive parts Tolcap can be used to find process capable tolerances for rotationally moulded thermoplastics with dimensions 100 to 4000mm.
SAN, styrene-acrylonitrile resin, styrene acrylonitrile plastic (thermoplastic): Good durability, heat and chemical resistant properties. A thermoplastic commonly used for food containers, water bottles, hygiene and sanitary products. Use Tolcap to work out suitable process capable tolerances for dimensions on parts involving extrusion, blow moulding, rotational moulding, precision injection moulding or injection compression of SAN.
Sand Casting ( Manufacturing Process ^{Ref 1} ): A metal pattern is coated in a moistened bonded sand. The pattern is removed and molten metal is poured in and left to solidify. The part is removed by breaking away the sand.
Materials: metals
Typical applications: engine blocks, cylinder heads Tolcap can be used to find process capable tolerances for sand cast aluminium, copper and magnesium alloys of dimensions 10 to 5000mm, and iron and steel 10 to 10,000mm.
Sheet Metalworking ( Manufacturing Process ^{Ref 1} ): A range manufacturing processes in which metal sheets are deformed or cut. Tolcap can be used to find capable tolerances for a wide range of sheet metal processes for steel alloy, medium & high carbon steel, mild steel, stainless steel; aluminium, copper, lead, magnesium, nickel, tin, titanium, and zinc alloys:

Deep Drawing

Ironing

Blanking

Bending

Cutting - Tolcap can be used to find process capable tolerances for cut sheet metal with dimensions 1 to 3000mm

Punching - Tolcap can be used to find process capable tolerances for cut sheet metal with dimensions 1 to 300mm

Roll Forming

Spinning
Sheet Metal Bending ( Manufacturing Process ^{Ref 1} ): A manufacturing process in which sheet metal is deformed to form angles or contours.

Materials: metals and alloy sheet
Typical applications: ductwork, cabinets, auto parts Tolcap can be used to find process capable tolerances for bent: steel alloy, medium & high carbon steel, mild steel, stainless steel; aluminium, copper, lead, magnesium, nickel, tin, titanium, and zinc alloys with dimensions 1 to 1000mm.
Shell Moulding ( Manufacturing Process ^{Ref 1} ): Resin coated sand is tipped onto a heated metal pattern. Sand close to the pattern sets to form a mould, excess sand is tipped off and the pattern removed from the mould. The mould is supported whilst the molten metal is poured in and cooled.
Materials: most metals
Typical applications: small precise parts, gear housings, connecting rods Tolcap can be used to find process capable tolerances for shell moulded aluminium, copper, iron, magnesium and steel alloys of dimensions 10 to 1500mm.
Significant Characteristic (SC): A Significant Characteristic (SC) is a feature of a material, process, or part - usually occurring at lower assembly levels - whose achievement of the specified requirement has a significant importance to achieving the desired final product fit, performance, service life, and/or manufacturability.
There are several variations on this definition, but in short, while all tolerances need to be met, some are readily achieved, others may not be, and where there is doubt, these should be identified as Significant Characteristics where the capability is to be demonstrated or necessary extra controls identified. Tolcap identifies Significant Characteristics: wherever process capability is predicted to be below target.
Related: Key Characteristic , Critical Characteristic
Six Sigma: See 6σ.
Six Sigma Green Belt: Non specialist employees responsible for implementing Six Sigma within manufacturing projects under the guidance of Six Sigma Black Belt overseers.
Six Sigma Black Belt: Six Sigma specialists responsible for overseeing the application of Six Sigma methodology to specific manufacturing projects.
SPC, Statistical Process Control: A method of statistically monitoring and controlling manufacturing processes to maintain quality. Tolcap's predicted values of C_pk have proved to have very close correlation (98%) with SPC results.
Spring back, springback: The tendency of an elastically deformed part to revert to its original form.
Spinning, Spin Forming, Metal Turning ( Manufacturing Process ): A manufacturing process in which a rapidly rotating disc or tube of metal is deformed to cover a mandrel of the required shape by means of pressure applied by a roller or rounded tool.
Materials: metals and alloy sheet
Typical applications: typically rounded, bell or conical shapes - nose cones, goblets Tolcap can be used to find process capable tolerances for spun sheet metal: steel alloy, medium & high carbon steel, mild steel, stainless steel; aluminium, copper, lead, magnesium, nickel, tin, titanium, and zinc alloys with dimensions 50 to 5000mm.
Stack: The interacting components of a manufactured part.
See also Tolerance Stack
Stack Tolerance: See Tolerance Stack
Standard Deviation: See σ.
Standards: Engineering standards are guidelines specifying characteristics and technical details that should be met when making products or utilising processes.

They are drawn up by a number of agencies worldwide.
Engineering tolerance related Standards include:

American National Standards Institute / American Society of Mechanical Engineers -
ANSI B4.1 and it's metric version ANSI B4.2 : Preferred Limits and Fits
ASME Y14.5-2009: Dimensioning and Tolerancing

British Standard -
BS 8888:2017 (which supersedes BS 308): Technical product documentation and specification
BS EN 20286 a British equivalent to ISO 286
BS EN ISO 2692: Geometrical product specifications (GPS). Geometrical tolerancing. Maximum material requirement (MMR), least material requirement (LMR) and reciprocity requirement (RPR).

Deutsches Institut für Normung e.V. -
DIN 16742 (which supersedes DIN 16901): Plastics Moulded Parts - Tolerances and Acceptance Conditions
DIN 1688-4 now withrawn: Light metal alloy raw castings; pressure die castings; general tolerances, machining allowances

International Organization for Standardization -
ISO 14405: Geometrical product specifications (GPS) - Dimensional tolerancing
ISO 286 (which supersedes ISO 1829): Geometrical product specifications (GPS) — ISO code system for tolerances on linear sizes
ISO 20457:2018: (progenitor DIN 16742) Plastics moulded parts — Tolerances and acceptance conditions
ISO 2768: General tolerances
ISO 8062: Geometrical product specifications (GPS) — Dimensional and geometrical tolerances for moulded parts Richard Batchelor discusses the relationship between Tolcap and Standards in a number of his Blogs:
Tolerancing from Standards? Use Tolcap for a fast route to the baseline.
Rough Guide to Tolerancing Plastic Mouldings - Tolcap or DIN 16901?
Subtractive Manufacturing Technology: Parts are created by removing material from solid blocks (blanks) e.g. by lathes, grinders, mills and routers.
Related Formative and Additive.
Surface Grinding ( Manufacturing Process ): An machining process in which an abrasive spinning wheel chips material from a workpiece. It is used to produce a smooth flat surfaces.
Materials: hard inflexible materials
Typical applications: bearing surfaces, gears, cams Tolcap can be used to find process capable tolerances for surface ground: steel alloy, cast steel, free cut steel, medium & high carbon steel, mild steel, stainless steel, tool steel; nickel, and titanium alloys; and grey, malleable, modular, and pearlite iron; with dimensions 1 to 1000mm.
Swaging ( Manufacturing Process ): A component is altered by forcing into a shaped die or mould. Swaging can be performed hot or cold.
Swaging can be Tube, Die, Rotary or Orbital.
Materials: Metals, alloys, plastics (hot)
Typical applications: circuit board connections, pipes, bullets

Related: Cold Forming. Tolcap can be used to find process capable tolerances for cold swaged medium & high carbon steel, mild steel, stainless steel, and alloys of aluminium, copper, lead, magnesium, nickel, steel, tin and zinc - for dimensions in the range 10 to 150mm.
Thermoplastic: A plastic material (polymer) that at specific temperatures becomes pliable and can be reshaped. On cooling the thermoplastic retains its new shape. If reheated thermoplastics will tend to regain their original shape.
Thermoplastics include ABS, CA, CP, PBT, PC, PCTFE, PE, PESU, PET (PETE), PF, PMMA, POM, PP, PPS, PS, PSU, PVC-U, SAN.

Related: plastic, thermoset. Tolcap can be used to work out process capable dimensional tolerances for parts involving extrusion, blow moulding, rotational moulding, precision injection moulding or injection compression of thermoplastics.
Thermoset: Plastics that can melted, or heated until pliable, and reshaped. On cooling the thermoset plastic retains its new shape. Due to new cross-links that form during curing thermoset plastics do not revert to their original shape on reheating (unlike thermoplastics).
Thermoset plastics include Epoxy, PA, PF, UP.

Related: plastic, thermoplastic. Use Tolcap to work out process capable tolerances for dimensions on parts involving injection compression of thermosets.
Tolerance: An expression of the acceptable variation in a manufactured parts dimension
e.g. a rods length might be specified as 10.0 ± 0.2cm meaning:
minimum acceptable rod length 9.8cm,
maximum acceptable rod length 10.2cm.
Tolerance Capability Expert, TCE: Tolerance Capability Expert (TCE) was the earliest, spreadsheet based, form of the software now known as Tolcap.
Tolerance Grades: International Standards terminology used to categorise materials into acceptable tolerance bands.
Tolerance Stack, Tolerance Stackup, Tolerance Stack-up: The accumulated tolerances in a manufactured part that comprises a number of individually toleranced interacting components.
The fourth of in Tolcap's video series deals with Tolerance Stacks. .
TPS, Toyota Production System: See JIT
Turning and Boring ( Manufacturing Process ^{Ref 1} ): Turning is a simple machining process in which material is removed by a single point cutting tool held against a rotating workpiece. Similarly, boring involves enlarging a drill created hole in a rotating workpiece. Materials: metals and alloys, hard plastics, wood
Typical applications: screws, bolts, shaped shafts Tolcap can be used to find process capable tolerances for turning and boring: steel alloy, cast steel, free cut steel, medium & high carbon steel, mild steel, stainless steel, tool steel; aluminium, copper, lead, magnesium, nickel, tin, titanium, and zinc alloys; and grey iron; with dimensions 5 to 5000mm.
And for ultra precise turning and boring with dimensions 1 to 1000mm.
Ultrasonic Impact Grinding ( Manufacturing Process ): Also known as Ultrasonic Machining.
Unfilled polymer: See Filled / Unfilled polymer.
Ultrasonic Machining, USM, Ultrasonic Impact Grinding ( Manufacturing Process ^{Ref 1} ): The workpiece is vibrated at ultrasonic frequency in an abrasive slurry removing material.
Materials: most effective with brittle materials, ceramics, precious stones, tool steels, titanium, glass
Typical applications: complex holes and cavities, coining Tolcap can help you establish suitable process capable tolerances for ultrasonic machined parts of dimensions 1 to 100mm.
UP, unsaturated polyester (thermoset): Hard durable thermoset plastics. Typically used in larger engineered items such as boat hulls, vehicle parts, shower trays and appliances. Use Tolcap to work out process capable tolerances for dimensions on parts involving injection compression of unsaturated polyester.
Upper Specification Limit, USL: See UTL.
Upper Tolerance Limit, UTL: e.g. A rods length specified as 10.0 ± 0.2cm has a UTL 10.2cm.
Worst Case Tolerance Stack: The tolerances of stacked manufactured components accumulated in such a way to present the worst possible mechanical outcomes
e.g. A rod needs to fit in a hole:

Diameter
(cm) Worst
Cases (cm)

Rod 1.0±0.1 0.9
(LTL) 1.1
(UTL)

Hole 1.2±0.1 1.3
(UTL) 1.1
(LTL)

Note Too
loose? Uncomfortably
tight?

Frequently quoted on the internet
Process Capability, C_p	Rejected parts per million (ppm)
0.33	317,300
0.67	45,500
1	2,700
1.33	63
1.5
1.67	0.6
2	0.002

Used by TOLCAP
Process Capability, C_pk	Rejected parts per million (ppm)
0.33	161,100
0.67	22,200
1	1,350
1.33	33
1.5	3.4
1.67	0.3
2	< 0.1

	Diameter (cm)	Worst Cases (cm)
Rod	1.0±0.1	0.9 (LTL)	1.1 (UTL)
Hole	1.2±0.1	1.3 (UTL)	1.1 (LTL)
Note		Too loose?	Uncomfortably tight?

References

Swift, K.G.* and Booker, J.D.
Process Selection: From Design to Manufacture,
2003. Oxford: Butterworth-Heinemann.

* Professor Ken Swift CEng, FIMechE, is a founding member of the Tolcap developing Capra Technology team. Ken specialises in capable design and manufacture for quality and reliability in engineering.

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