The Importance of Uniform Wall Thickness in Plastics

Keeping the walls of your injection molded plastic part the same thickness is important for maintaining good cosmetics and structural integrity. In this article, we’ll explain in depth why uniform wall thickness is so important.

Preventing Sink Marks

The number one reason to maintain uniform wall thickness is to prevent sink marks (also called “shrink marks”). Sink marks usually manifest as small depressions on a part, in areas which should be uniformly flat. They are often caused by non-uniform wall thickness creating non-uniform cooling of the center of the wall (since heat from the center takes longer to escape through thicker sections of plastic). This non-uniform cooling in turn creates non-uniform shrinkage, because not all areas of the part solidify at the same time. When the still liquid plastic in the center shrinks and solidifies, it pulls on the neighboring areas which have already solidified, causing them to cave in.


Choosing the Correct Tool Cavitation

Injection molding is great way to produce lots of plastic parts very rapidly and economically. What OEM’s often overlook, however is one key question which could make this great method even better:

How many cavities should there be in injection molding tools making our parts?

Answering this question can be the key to getting the most return from the OEM’s production cost as well as the contract manufacturer’s machine time. Deciding how many cavities per tool is all about making tradeoffs between the price per part, production time, and initial tooling cost in order to reach the lowest total production cost for producing quality parts. Lake many other optimization challenges in manufacturing, it requires close collaboration between contract manufacturers and OEM’s, engineers and management.


The Importance of DFM Analysis for Injection Molding

An ounce of prevention is worth a pound of cure. Or several pounds of scrapped parts. Of all the design requirements, meetings, specifications and documentation involved when it comes to injection molded plastic parts, one of the most critical elements of the design process is often skipped: a formal Design for Manufacturing (DFM) analysis.

When OEMs and contract manufactures skip this step, an opportunity is lost to combine engineering and manufacturing expertise to detect manufacturing issues and correct them before significant costs are incurred. Besides avoiding costly tooling modifications down the road, input receive from formal DFM analysis can also decrease part weight and cycle time, as well as improve the structural integrity of the part—all with slight modifications to the original design.


Using Core-outs to Reduce the Weight of Plastic Parts

What’s a Core-out?

Core-outs are sections of a plastic part where a thick section of solid material has been replaced by square, rectangle, or hexagonal sections. This effectively replaces that solid material with empty voids surrounded by walls and ribs of uniform thickness. The core-outs themselves are usually placed on non-cosmetic surfaces, with the open areas facing down (like the underside of a handle) so that you don’t inadvertently create cubbies for dirt, dust, fluids or other unwanted material.

Carefully removing sections of a solid object is not an idea specific to injection molding of plastic parts. For example, many 3D printers (and their associated modeling software) have options for “sparse fill”: using a honeycomb or other structure with plenty of hollow space in places that would normally have solid material. In fused deposition modeling (FDM) 3D printers—where objects are built up layer by layer through extruding molten plastic through a small nozzle—this drastically shortens the amount of time need to print an object and reduces the amount of filament consumed during the print.


Medical Device Contract Manufacturing — When Less is More

In the highly competitive industry of medical devices, outsourcing is almost required to stay ahead. Its benefits are evident — multidisciplinary expertise, cost savings, flexibility, expansion, reduced risk, increased innovation, and quality assurance to name just a few. As a highly competitive industry, there is a plethora of medical device contract manufacturers available in all sizes. What size will suit you best?

Is Bigger Always Better?

It’s easy to find large medical device contract manufacturers. Their high-volume marketing budget allows them to promote their services world-wide and with an excessively large customer base they may be a “household name.” Some are industry giants! But bigger may not always be better for the majority.



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