Top tips to getting your parting line right
Parting lines are one of the main aesthetic problems that can happen with injection-molded parts.
It is possible to reduce the appearance of the parting lines on your components by working closely with your molding manufacturer. By combining your vision for the component and your designs with the molder and their expertise, the injection molding process and mold design can be adjusted to make sure the aesthetic impact of parting lines is reduced as much as possible.
What causes a parting line?
With injection molding parts it’s impossible to avoid creating a parting line. This is because it is caused during the molding process when the two parts of the mold, the clamp and the cavity, come together to shape the molten plastic. The meeting point between both parts of the mold is where the parting line appears on the product.
Depending on the tolerance and design of the mold and the particulars of the process, the parting line will be more or less obvious. However, due to the use of molds in the injection molding process, it will always be present.
How do parting lines affect the final product?
As well as impacting on the final aesthetics of a product, the position of the parting line can also affect the quality and strength of the part too. Between the product designer and the manufacturer, there are a few points that must be considered when developing a mold as part of a custom solution.
• As molten plastic is injected into a mold, the mold’s shape will affect how the plastic distributes across it. It will also affect how quickly the plastic cools and the number of layers of plastic that solidify and cause friction, otherwise known as the shearing rate. A high shearing rate can cause stresses in the part, so it’s an important consideration to make when thinking about its function and robustness.
• Once the molding process is complete and the mold separates, the machine will leave traces left by the separation of the mold halves and the ejection of the part from the mold. The shape of the mold and the design of the ejection process need to be considered to help reduce the potential for aesthetic damage.
• The location of the parting line in a mold can also have a significant impact when it comes to production cost. Depending on the complexity of the mold, deciding how the two halves will be split will be a challenge to balance aesthetics with part quality. The mold design will also affect the finishing processes needed to get the desired part aesthetics, which again will affect process and cost.
How can manufacturers help reduce the parting line?
Manufacturers are experts in their injection-molding processes. This means they can help to develop a mold for your design and create a part that is aesthetically pleasing and robust as well as being made cost effectively.
By working with your manufacturer to create your part mold, you can also work together with them on the injection-molding process itself, making sure that the amount of extra processes and flash (excess material that escapes from the mold) is reduced as much as possible.
To make sure that you utilize their expertise effectively, get in touch with your manufacturer at the design stage. That way they can advise you from the start (and maybe even help with prototyping) so you can be sure to get the part you want for the right price.