Selecting the right plastic injection mold maker can be challenging — but it doesn’t have to be. The most important part of finding the right partner for your project is knowing what qualities to look out for, and what services they need to provide. And, in this post, we’ll cover what those are. Here are the six key factors to consider when choosing a plastic mold maker:
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Working with a mold maker is likely going to be the start of a long-term partnership, which means that the company you consider needs two critical capabilities. These are exceptional customer service and clear and consistent communication.
This is vital, especially with complex mold designs, or projects that have a high level of intellectual property sensitivity. These two qualities will ensure that your partner is responsive to your needs and that their mold-making process is proceeding as it should be.
Be sure to ask your contact to walk you through the mold-making process — from placing your order, and through the whole series of manufacturing and delivery. And, pay attention if your contact can show a communicative process, and can break down any industry terms into language you can easily understand.
These are good signs that the company is professional, open to communication, and can include you in every step of development with ease.
While it is a given that you will have to make concessions with your partnered mold maker, having to compromise too much might put you in a challenging situation.
Regardless of what designs you want for your plastic product, there is going to be a company that can balance practicality with the vision you have in mind. A good plastic injection mold maker can make strong recommendations to improve your design’s manufacturability and functionality, without asking you to make too many compromises.
These recommendations may include minor design tweaks, alternative resin suggestions, and other ways that can help you save time and money with your mold and your plastic injection molding process.
Not all mold makers have expanded services and technology to make durable, precise, and high-quality plastic molding and tooling.
So, selecting a plastic injection molding company that not only has a great design team to help you improve your mold but also has the capabilities to add to their mold-making process is important.
Working with a mold maker who offers services such as in-depth mold flow analysis, quick response manufacturing, several mold materials, part design services, and more will help you make your mold as cost-efficient as possible while meeting your exact design specifications.
As we mentioned earlier, your injection molding partner needs to offer quality services, as well as efficiency when creating your requested mold.
Here are a few indicators of an injection mold maker that can offer you both of those qualities in their services:
Price is always an important factor when choosing a partner for manufacturing — it’s part of staying within budget, and calculating the best return on investment.
However, always going for the bargain deals may cost you more in the long run. When it comes to mold making, many elements come into play when tallying up the overall price, including added services and design optimization.
Sometimes, a more costly investment just means you’re paying for good design and material selection, as well as valuable support from your mold-making team.
When receiving a quote, always consider the overall value of the mold and service being provided, as well as the mold maker’s ability to be a vital resource to you and your team before signing on or writing them off.
Many things will add to a mold maker’s ability to deliver an exceptional design and product, but the most important one will always be the years of experience they have in business.
When looking for a mold maker, always consider how long they have spent in the industry. Be sure to ask how long the company has been offering their mold-making services, and also ask what specializations or expertise they have.
Choosing the right mold maker is crucial to the success of your final plastic product. Keep these factors to consider when choosing a plastic mold maker in mind to find the right partner that can meet your specific needs, and understand your expectations and challenges.
The injection molding process is widely used in large volume production as it produces comparatively low scrap production and has high repeatability. The versatility of the injection molding process demands much broader design considerations. Most of the design considerations will be made on the mould after setting out the product requirements.
Some of the factors that affect the injection molding design include: how the part will be used (singular product or for assembly), its dimensional and mechanical requirements, and its ability to withstand elements such as chemicals or pressure. Some vital tips to consider when designing for injection molding are explored below.
Different injection molding materials offer varying properties. For example, some injection molding materials provide more dimensional stability than others. Similarly, some bond better with adhesives than others. Material design considers the following: temperature, pressure, biological and chemical interactions.
Thermoplastic resins can be broadly classified into amorphous and semi-crystalline. While semi-crystalline thermoplastics offer better chemical and electrical resistance, their amorphous counterparts are much more dimensionally stable and more resistant to impact. Material selection can affect the required tolerance level or certain features, like wall thickness.
Tolerances are affected by the shrinkage that occurs during the cooling process. Amorphous materials like PLA generally have tighter tolerances than semi-crystaline materials like PEEK.
Tight tolerances make production more expensive, but they may be necessary for your part to fit or function properly, especially if it is used in an assembly.
We recommend contacting your supplier at the design stage to discuss the tolerance standards that they use.
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For example, DIN contains a general tolerance table as a reference for different materials. If your supplier uses this standard and you need tighter tolerances or other standards, they will ask you to provide 2D drawings.
There are a few key points to consider to ensure you choose the right wall thickness for your injection molding design:
The following are the recommended wall thicknesses for different materials:
Many material removal processes such as CNC machining can produce vertical walls. However, creating a part’s design for injection molding with vertical walls will cause the part to get stuck, particularly at the core, as the part contracts on cooling.
If too much force is applied to eject the part, the risk of damaging the ejector pins and even the mould becomes very high. Design the walls of parts with a slight slant to avoid this problem. This slanting is called a draft.
Due to the high complexity, it creates in designing, the draft is usually added at the final stages of the part design. Different surfaces require varying drafts. Textured surfaces require the most draft. Some common surfaces found in injection molding and their minimum draft angles are as follows.
Certain parts require ribs. Ribs and gussets give additional strength to parts and help to eliminate cosmetic defects like warping, sink and voids. These features are essential for structural components. Therefore, it is preferable to add them to parts rather than increase the thickness of parts to increase strength.
However, if not properly designed, this can lead to shrinkage. Shrinkage happens when the cooling rate of certain parts is much faster than others, resulting in the permanent bending of some sections. The warping can be effectively reduced by keeping the rib thickness between 50 – 60% of that of the wall it is attached to.
Applying radii to parts, when possible, eliminates sharp corners, which improves the flow of material and the part’s structural integrity. Sharp corners cause weakness in the part as the molten material is made to flow through the corner or into the corner. The only places where sharp corners are unavoidable are the parting surfaces or shut-off surfaces.
Radii and fillets also aid in a part ejection as rounded corners are less likely to get stuck during ejection than sharp corners. Furthermore, sharp corners are also not structurally advisable as they lead to stress points that can fail. Radii help to smoothen out the stress on the corners.
Also, including sharp corners in your part will exponentially increase the cost of production as this would require the mould to feature sharp corners that can only be achieved using very expensive manufacturing techniques.
Add internal radii at least 0.5 times the thickness of the adjacent wall and external radii 1.5 times the size.
Snap fits are obtainable through undercuts. The straight-pull mould, which consists of two halves, and is the most straightforward design, is not suitable to manufacture parts with undercut features. This is due to the difficulty in machining such a mould with CNC and the tendency of the material to get stuck on ejection.
Undercuts are usually created using side cores. However, side cores significantly increase tooling costs. Luckily there are some design tips to achieve the function of an undercut without using side cores. One way of doing this is by introducing a slot instead.
This is also referred to as a pass-through core. Another way is to adjust or move the parting line of the part. When doing this, also adjust the draft angle accordingly. Moving the parting lines is most suitable for undercuts that are on the outside of the part.
You can also use stripping undercuts, also referred to as bump offs. However, only use this feature when the part is flexible enough to deform and expand during ejection from the mould.
Also, give enough clearance: bump-offs must have a lead angle of 30° to 45° for effective ejection. All these alternatives to expensive side cores require significant redesigning of the part. When the redesign of a part is not possible due to the possibility that it may affect the functionality of the part, then you have to employ sliding side-actions and cores to deal with undercuts.
These features slide in as the mould closes and slide out as it opens. The side cores must move perpendicularly and have appropriate draft angles.
Bosses are cylindrical standoffs moulded into a plastic part to accept an insert, self-tapping screw, or pin for assembling or mounting parts.
The outer diameter (OD) of the boss should be 2.5 times the diameter of the screw diameter for self-tapping applications.
Bosses shouldn’t be freestanding. Always attach bosses to a side wall or to the floor with ribs or gussets. Their thickness should not exceed 60% of the overall part thickness to minimize visible sink marks on the outside of the part.
For example, a part with an outer wall of 3 mm should have internal ribs that are no more than 1.7 mm thick.
In order to properly design and manufacture your part using injection molding, it is important for the manufacturer to understand from the outset what your requirements are in terms of its appearance.
One key point for the tool maker to consider is the gate location. Gates are entry sections through which the molten material enters the mould. The tool maker has to choose the type of the gates and position them strategically to minimize potential quality issues.
Gates also leave gate vestige or a visual indication that the part was gated—even if it is subtle.
That’s why we recommend letting your supplier know about any aesthetic and functional requirements and defining where not to gate.
At Xometry Europe, we offer injection molding services with over 30 materials, such as plastics, synthetic and silicone rubber, and elastomers. Simply head over to our Quoting Engine to upload your model and select your part preferences to receive a 24h quote.
If you are looking for more details, kindly visit Plastic Injection Molds.