An overview of the design process

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injection molding

For a design to be successful, all the necessary information must be available before beginning. If this simple rule is ignored, many bad things can happen, such as poor designs, misunderstandings, poor component quality, and disputes between suppliers and end users.

Experienced designers will almost certainly follow all the steps to avoid pitfalls, but even then, they may run into obstacles from time to time due to the sheer number of potential pitfalls. As a result, it is advantageous to have a checklist that can be added to at any time and can be checked off point-by-point to ensure that nothing is missed.

Creating a Checklist Before Design:

  • Original estimate details
  • Diagrams of components
  • Component dimensions
  • Material for the component
  • Amount necessary
  • Purpose of components
  • Product tolerances
  • Impression count
  • Gating
  • Ejection
  • Appearance of component parts

Guide to Designing Moulds

  • Original Estimate Details

1. From the very beginning it is important for the designer to have access to the original estimate details. This information should provide the designer with all the details required to complete the design.

2. Whenever there are any questions or omissions of information, these should be brought to the estimator’s attention as soon as possible. A mould tool design cannot begin without a clear design brief.

3. When an estimator prepares a quotation, this does not mean the value judgements are fixed. It is very common for estimates to be prepared in a short period of time and as a result they may not be as fully thought out as they would be if they had had more time. Therefore, the designer should not immediately accept the estimate details and should challenge any claims that seem questionable or even inaccurate.

  • Diagrams of components

1. The component drawing should be fully detailed. There must be no room for ambiguity or misinterpretation. Dimensions, tolerances, and materials must all be specified to the letter.

2. It is the designer’s responsibility to address any doubts the customer may have, and to issue a new drawing after discussing and agreeing with the customer.

3. Both the supplier and the customer must work from the same drawing. If they don’t, confusion, delays, costly mistakes, and disagreements will result.

  • Component dimensions

1. Until the designer understands the customer’s requirements completely, he must carefully examine the drawing. That is an essential step. The type of mould tool that is needed will be determined by this analysis of component form. Examples include two-plates, three-plates, hotrunner, side sliders, lifters, stacks, and so on.

2. Injection moulding may not be possible for some component geometries. It must be communicated to the customer immediately if this is true. The component might be made by assembling different moulds. Regardless of the outcome, this is an extremely important issue requiring immediate attention.

plastic mold
plastic mold

An overview of the design process

  • Material for the component

1. All designs require an understanding of materials characteristics. Material specifications must be precise and explicit. The designer should ask the customer about the material, since he may already be intimately familiar with it, or ask the supplier for more information if he is unfamiliar with it.

2.Check whether the material can be injected. If the moulders cannot reach the high temperatures and pressures required by the product, they may be unable to use their machines.

3.Similarly, the material might not be an appropriate choice for the intended application due to its performance requirements. There could be brittleness, softness, or insufficient strength.

4.A cheaper alternative may be available if the material is very expensive. In addition, it is possible that the moulder already holds a large inventory of stock materials that they are familiar with. Inquiring if such a material can be used in a satisfactory way.

5.Performing the same task as an alternative is always worth it regardless of its equivalent

  • Amount necessary

1. As the quantity often (but not always) determines how many cavities the mould tool will leave, it is another important factor.

2. The type of tool used may also be determined by this factor. If the quantities are high enough, for example, a hot runner or runnerless tool could be used.

  • Purpose of components

1. The customer will use this component in a certain way. If a customer requests a material, the moulder should ensure that it can be used for the application.

2. It is often the case that the customer selects a material that is unsuitable for the application, which leads to problems and even failures.

3. A customer may have been unfairly influenced by a material manufacturer in some cases. However, other materials may be better suited to the job, or a cheaper alternative may be better suited for the task as well.

Mould Design Guide

  • Product tolerances

1.  Molders must ensure that the drawings are accurate in order to meet production tolerances.

2.Tolerances of a small size make molding an extremely challenging process. The designer should take less cavities when close tolerances are present than otherwise necessary. 

3.Molding tolerances increase with the number of cavities during the moulding process. It is common to encounter many problems with out-of-tolerance parts when molding on large numbers of cavities with closely toleranced dimensions.

  • Cavities count

1. It is common for the original estimate to be based on the customer being given an alternative number of mould cavities. Prior to beginning the design process, it is essential to inform the designer which of these alternatives the customer has chosen.

2.The designer should challenge the number of cavities immediately if they believe it is excessive.

3.Tolerance considerations and machine clamping limitations can all be considered when challenging the number of cavities. 

  • Gating

1.This is another significant factor that determines whether a mould tool will be successful. You should choose the type of gates and where to place it cautiously.

2.It is important to choose the gate type and position in order to achieve a solid moulding. Due to functional or aesthetic reasons, the gate often needs to be moved. In cases where the gate has to be placed in a dubious position, the designer should challenge this as soon as possible.

3.Delegation of the component is also subject to similar considerations. Auto de-gating is always a good idea. Degaging fixtures and jigs need to be designed for self-degating if this cannot be accomplished.

  • Ejection

1. Method selection will be influenced by one or more factors, such as the material, component geometry, and other factors like mould friction and drag.

2. An attempt should be made to ensure that all the components are ejected from the mould tool in a positive and balanced manner. A moulding machine’s capabilities and ejector arrangements will vary depending on its design and ejector arrangement, for example, whether a core-pulling or hydraulic ejector arrangement is available.

3. Customer acceptance of witness marks should be verified. There should be no witness marks on component appearance faces or on the functional surfaces, for example.

4. Ensure that draft angles appear on the drawing of the component. Those who are not present for the customer to negotiate should be deemed necessary if they are not present.

  • Appearance of component parts

1. There are many faces that are an important part of one’s appearance, which causes mouldings to be used in those situations. To prevent potential undercutting and drag witness marks, the tool cavities must be designed with this in mind.

2. It may be necessary to fabricate the cavity construction in order to achieve textured areas.

3. Taking into account the gate position, ejection lines, and split lines will also have to be considered. Split line/ejection systems must be checked carefully for witness marks and drag.

4. Furthermore, the appearance of a mould will be influenced by the cooling design and its efficiency.

 

 

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