Speed up the design of new parts for plastic injection molding
How to ensure the design is suitable for plastics
Designing a part requires a great deal of know-how and experience. To save on costs and time, injection molders must ensure that the number of correction loops required to observe the tolerances and attain the quality requirements is kept to a minimum. When compiling a new design for a part to be produced by injection molding with only a short period of time available for the design process, it is very useful to have rules that will ensure the design is suitable for plastics.
The following rules exist for a design tailored to plastic:
a. Keep wall thicknesses as small as possible
b. Use uniform wall thicknesses
c. Avoid accumulations of material
d. Provide radii on corners and edges
e. Use a rib design suitable for injection molding
f. Avoid flat surfaces
g. Ensure sufficient conicity
h. Avoid undercuts
i. Ensure that machining does not have to be more precise than really necessary
j. Exploit the potential of injection molding to the full
There are usually several different reasons for these individual design rules. A number of the rules are taken up below, showing you how to use them to speed up the compilation of new designs:
1. How to eliminate sink marks
Sink marks develop as a result of accumulations of material (c):
- Edges are accumulations of melt à provide them with radii (d)
- Ribs à tailor their design to the injection molding process (e)
- Design uniform wall thickness or wall thicknesses so that they can be adequately supplied by holding pressure
Avoid sink marks right from the outset with CADMOULD:
Accumulations of material can be readily localized on the wall thickness display in CADMOULD. A check can then be conducted to see whether an accumulation of material occurs on the opposite side of a rib. In addition, there are various simulation results that can be used to evaluate the characteristics of sink marks. On the right side, you can see a simulation example for a sink mark created by melt accumulation.
2. How to optimise shrinkage and warpage
- Rule of thumb: the part warps towards the hotter side
- Avoid flat surfaces (f), since curved or ribbed surfaces offer greater dimensional stability.
- Provide uniform wall thicknesses (b), since uneven cooling will otherwise result and hence uneven shrinkage à warpage
- Provide radii on corners and edges (d) so as to ensure more uniform cooling
- Design ribs so they are tailored to injection molding à avoid uneven cooling and hence warpage
In CADMOULD, you can realistically depict the shrinkage and warpage of the part in a diagram and make the necessary changes. You can check the extent of shrinkage that would occur with the specified parameters and then simulate the compensation required in the mold.
3. Can the part be produced by injection molding?
- Demolding drafts need to be incorporated (g) and undercuts avoided (h) so that the part can be demolded and does not remain stuck in the mold.
Determining feasibility with CADMOULD: a check can be conducted on both demolding drafts and undercuts with the aid of the feasibility analysis in CADMOULD. These can then be modified prior to the first injection molding test.
4. How can a newly designed part be produced in a more cost-efficient manner
- Keep the tolerances as small as possible (i)
- Fully exploit the potential of injection molding
Produce the new design economically with CADMOULD:
The prediction of shrinkage and warpage in CADMOULD enables the true shape of the part to be estimated. This ensures that the tolerances are not set any higher than is necessary. In addition, the integration of a large number of technical functions (e.g. seals, fastening elements, suspension, hinges, etc.) in the plastic component can save a large number of the work steps that are needed in conventional processes. While this increases the complexity of the part, it saves a great deal of time and money later on. The simulation also helps secure the quality of the part despite this! Without simulations, it would be virtually impossible to design parts of such complexity.