Tolcap enables designers and engineers to allocate working tolerances to part dimensions for over 80 manufacturing processes. Tolcap version 2 (V2) includes new ways to tolerance plastic mouldings in generic materials.
In his blog series, Richard Batchelor discussed how to find capable tolerances for your plastic moulded parts employing Tolcap from a DIN 16901, DIN 16742 or ISO 20457 starting point. These considerations were limited to plastic materials specifically featured in one of the Tolcap version 1 (V1) 'Injection or compression moulding' graphs:
Tolcap V2 introduces ways to estimate tolerances, or process capabilities, for moulded parts in plastic varieties not specifically named in Tolcap's empirically verified graphs - either by employing DIN/ISO Standards or, where Standards information is unavailable, by using material shrinkage information.
(The techniques discussed in this Blog are also outlined within the Tolcap V2 inline Help - see 'Plastic Moulding'.)
Some things haven't changed
Tolcap V1 contains five established and validated 'Injection or compression moulding' Tolerance vs Dimension maps which cover: ABS, CA, CP, EPOXY, PA, PBTP, PC, PCTFE, PE, PESU, PETP, PF, PMMA, filled POM, PP, PPS, PS, PSU, PVC-U, SAN, and UP. Tolcap V2 also contains these maps (note - we've tweaked the process names):
These process maps are applicable to single or multi-cavity tools for volume production of plastic parts.
Immediately below the highlighted section in the screenshots above you can see Tolcap V2 also retains V1's 'Injection mouldings for precision engineering components (All thermoplastics)' map.
So what is new in Tolcap's Plastic Moulding processes?
Tolcap V2 features three new 'Injection / Compression Moulding' process maps:
The following 3 maps enable you to estimate tolerances for plastic moulding materials not specifically named in a Tolcap process.
- Injection Moulding Low Shrinkage (& DIN/ISO Cross Ref)
- Injection Moulding Medium Shrinkage (& DIN/ISO Cross Ref)
- Injection Moulding High Shrinkage (& DIN/ISO Cross Ref)
If your intended production plastic is not listed in Tolcap's old 'Injection / Compression: <Named Material>' processes, follow the links below to the appended sections of this blog - where we detail how progress may be made starting from the international standards:
or by reference to the:
Why bother with Tolcap when you have access to a standard?
Tolcap offers you a number of advantages over straight DIN/ISO Standard use:
- Greater flexibility in dimension entry.
- Straightforward process capability, Cpk, alterations or assessments.
- Quick checks of anticipated parts per million rejects.
- Saved calculations for future reference.
- Allowance for issues with manufacturing conditions via Tolcap's 'Additional Variation Wizard':
Tolcap's Additional Variation Wizard - Adjustment for anticipated complications in part geometry via Tolcap's 'Geometry Wizard'.
As with the DIN / ISO Standards Tolcap can make allowance for parting line effects, but Tolcap allows you to make allowance for many other factors:
Tolcap's Geometry Effect Wizard
Tolerancing your plastic component starting from DIN16901 or DIN16742 / ISO20457 or material shrinkage
Match to a Tolcap map using DIN16901
(The relationship between DIN16901 and Tolcap is considered in more depth in the blog: The Tolcap Rough Guide to Tolerancing Plastic Mouldings - Tolcap or DIN16901? )
The DIN16901 standard is now superseded (final edition 1982) but remains familiar to many. It lists many materials not featured in Tolcap V1's 'Injection / Compression: <Named Material>' processes.
How the DIN16901 Standard is typically used to find tolerances:
For each of its listed materials, DIN16901 specifies three Tolerance Groups:
- General tolerances
- Series 1: Tolerances achievable without special measures
- Series 2: Tolerances achievable with special measures
From a table of data, each Material / Tolerance Group combination is assigned a three digit code: 110, 120, 130, 140, 150, or 160.
A second table, with rows numbered 110, 120 ... 160, is then used to suggest suitable tolerances for specified dimensions.
Using the DIN16901 Standard in conjunction with Tolcap:
For the intended manufacturing material:
- Use the first DIN16901 Standard table to establish the three Tolerance Group codes.
- Rather than use the second DIN16901 table, employ Tolcap using the following DIN16901 Tolerance Groups to Tolcap Process correlation:
| DIN16901 Tolerance Groups | Use Tolcap Process | ||
|---|---|---|---|
| General tolerances |
Series 1 | Series 2 | |
| 130 | 120 | 110 | Injection Moulding Low Shrinkage (& DIN/ISO Cross Ref) |
| 140 | 130 | 120 | Injection Moulding Medium Shrinkage (& DIN/ISO Cross Ref) |
| 150 | 140 | 130 | Injection Moulding High Shrinkage (& DIN/ISO Cross Ref) |
e.g. for EVA - 140, 130, 120 - use Tolcap's 'Injection Moulding Medium Shrinkage (& DIN/ISO Cross Ref)' process.
Adjust for part geometry and manufacturing conditions
On Tolcap's 'Injection Moulding Low / Medium / High Shrinkage (& DIN/ISO Cross Ref)' Process maps, the Cpk=1.33 line contours closely with DIN16901's third Tolerance Group. DIN16901's third Tolerance Group corresponds to tolerances that 'may need special measures', hence to find tolerances that do not need special measures there is margin for the addition of Tolcap's Geometry Effect and Additional Variation allowances.
Match to a Tolcap map using DIN16742 / ISO20457
(The relationship between DIN16742 / ISO20457 and Tolcap is considered in more depth in our blog: The Tolcap Rough Guide to Tolerancing Plastic Mouldings - Tolcap or ISO20457 or DIN16742?)
How the DIN16742 / ISO20457 Standard is used to find tolerances:
The newer Tolerance Standards DIN16742 (2013) and ISO20457 (2018) do not list specific materials, but guide the user through an algorithm to work out Tolerance Grades from properties of the material including the material stiffness, and/or hardness, and the moulding shrinkage.
Using the DIN16742 / ISO20457 Standard in conjunction with Tolcap:
Apply the DIN16742 / ISO20457 algorithm to the materials properties to obtain the Tolerance Grade references (TG1, TG2 ... TG8) for:
- Series 1: For Simple Production
- Series 2: For Accurate Production
(Series 3: For Precision Production is not required)
Progress your tolerance investigations by selecting the appropriate Tolcap Process from the correlation with DIN16742 / ISO20457 tolerance grades in the table below:
| DIN16742 / ISO20457 TG Code | Use Tolcap Process | |
|---|---|---|
| Series 2: Accurate Production |
Series 1: Simple Production |
|
| TG4 | TG5 | Injection Moulding Low Shrinkage (& DIN/ISO Cross Ref) |
| TG5 | TG6 | Injection Moulding Medium Shrinkage(& DIN/ISO Cross Ref) |
| TG6 | TG7 | Injection Moulding High Shrinkage (& DIN/ISO Cross Ref) |
e.g. For PA, polyamide, DIN16742 gives an Accurate Production code of TG5 and a Simple Production code of TG6. Tolcap's 'Injection Moulding Medium Shrinkage (& DIN/ISO Cross Ref)' Process map at Cpk=1.33 contours closely to the DIN16742 TG5 Tolerance Grade values.
Adjust for part Geometry and Manufacturing conditions
The 'Injection Moulding Medium Shrinkage (& DIN/ISO Cross Ref)' Tolcap Process corresponds to Accurate Production for polyamide, there is margin for the addition of Geometry Effect and Additional Variation allowances to find tolerances that will be capable for Simple Production.
Make a first tolerance estimate based on material shrinkage
The relationship between Plastic Shrinkage and Tolcap is considered in more depth in our blog: The Tolcap Rough Guide to Tolerancing Plastic Mouldings - Tolcap or ISO20457 or DIN16742?
Where:
- no Tolcap map exists for a specific material
- Standards information is unavailable
- and material properties data is limited
- it may be possible to obtain a first estimate for tolerance based on material shrinkage.
Material shrinkage information is commonly available on the internet. For a first tolerance estimate based only on material shrinkage data use the correlation below:
| Material Shrinkage | Use Tolcap Process |
|---|---|
| < 1% | Injection Moulding Low Shrinkage (& DIN/ISO Cross Ref) |
| > 1% and < 2% | Injection Moulding Medium Shrinkage (& DIN/ISO Cross Ref) |
| > 2% | Injection Moulding High Shrinkage (& DIN/ISO Cross Ref) |
Notes
Many thanks to Ian Maynard CEng MIMechE for his support in our plastic tolerancing considerations (www.IanMaynardCEng.com).
Related blogs
‘The Tolcap Rough Guide to Tolerancing Plastic Mouldings’ series (Dec 2019):
- This Blog 1: Tolcap or DIN 16901?
- Blog 2: Tolcap or ISO 20457 / DIN 16742?
- Blog 3: Geometry and Process Effects