Specifying metal inserts for moulded plastics 20 December 2019

Choosing the wrong insert for the application can significantly increase costs, scrap rates, the risk of product failure, and manufacturing downtime. While often viewed as commodity items, inserts are integral to the design and manufacturing of many moulded plastic products. OEMs and plastic moulders are now teaming up with insert manufacturers to ensure they are properly sourcing the most ideal insert to handle a variety of applications.

Metal inserts are integral to the design and manufacturing of many moulded plastic products. Yet, because inserts are often viewed as commodity items, it is not uncommon for product designers to write up basic specs for an insert without confirming that the insert selected is in fact the most suitable for the product and its application. With the number of inserts required often reaching the millions, failure to source the most ideal insert can significantly increase costs, scrap rates, the risk of product failure, and result in excessive manufacturing downtime.

To solve this issue, many OEMs and plastic moulders have discovered that teaming with insert manufacturers that offer engineering expertise throughout the design and manufacturing process can be worth its weight in gold. This not only creates an extension of the OEMs own technical team, but can assist in the discovery of non-standard insert designs that can overcome wear problems, improve performance or longevity, and provide major cost savings in the long run.

Solution teamwork
For Carlton Tanner, senior manager at Blackland Precision Hardware, a Texan-based distributor of electronics and commercial hardware, rivets and inserts, this is an all too common occurrence where he and an insert supplier team up to assist an OEM that is having issues with the inserts they selected.

“This is particularly the case when the OEM gives us an insert order for a new product and the specs are sketchy, which happens fairly often,” says Tanner.

Since there are literally thousands of insert options available with each one designed to meet certain application requirements, it’s not always as simple as specifying OD, ID, length and thread count.

Tanner emphasises that even the most knowledgeable customers are wise to heed the advice of insert experts on their designs. He describes one such instance where an injection moulder working for a major automaker had specified a threaded brass insert with diamond knurling for a new product they were set to produce.

“Fortunately, the OEM conducted an initial test with the insert, where it became evident that the design they selected was somewhat problematic for their production process,” Tanner explains. “Before they could place the million-plus part order, they needed a solution, fast.”

Fearing the issue could force production backups, cost run-ups and missed deliveries for the OEM, Tanner took the issue to one of his primary insert suppliers, Tri-Star Industries. Tri-Star specialises in threaded inserts and compression limiters for plastics. It has an extensive catalogue of available items as well as hundreds of custom inserts it has designed since the 1990s.

“What we found was that the knurled surface of the inserts was chipping slightly, both in transit and as the inserts were bulk-loaded into the injection moulding system (a standard operation. As a result, the accumulation of these small chips was effectively gumming up the automated injection moulding process, causing expensive unplanned downtime.”

Tri-Star’s technical support team evaluated the specs from the injection moulder and considered the end products various requirements before developing drawings for Tanner to review with the moulder. Those included a novel idea to modify the knurling, or the grooved pattern (often diamond-shaped) on the outside of the insert that helps keep it place.

Additionally, to prevent any minor chippings during shipment from entering the production, Tri-Star had another creative and yet cost-effective idea. They suggested adding a layer of mesh to the bottom of the insert shipping container, and an adhesive coating to the bottom of the container. The mesh would function as a sieve, through which the chips are able fall during transit; these errant chips will then stick to the adhesive surface on the bottom of the container.

“These were inventive solutions and effective as well,” says Tanner. “In fact, we never even had to use the adhesive backed mesh solution because their initial idea to modify the knurls worked so well. As a result, our customer’s manufacturing problem has been solved.”

The stainless solution
In another instance, an OEM/plastics moulder was sourcing inserts for use in commercial juice dispensing machine assemblies, the type often seen in cafeterias and restaurants.

“Since orange and grapefruit juice are highly acidic, this issue was that they would eventually cause a corrosion problem with a metal insert,” explains Aaron Edelson, Tri-Star’s sales engineer. The beverage dispenser OEM had specified an insert that required an expensive, secondary plating operation that insured a corrosion resistant barrier was present.

“I typically review the specifications on each customers’ orders and RFPs to make sure that the insert selected is not only suitable for their applications but offers the most cost-effective solution,” says Edelson.

In this case, he recommended that the customer use a stainless-steel insert instead. This would make it essentially impervious to corrosion, and thereby protect the juices from any impurities that would result from corrosion.

“Inserts composed of stainless steel are not available from the majority of insert manufacturers, so the OEM was amazed that it was even an option. Even though stainless steel is somewhat more expensive than common steel, we saved the OEM both the added time and expense of a secondary operation. With the large order they required, this added up to a huge savings.”

He adds that the demand for stainless steel is significantly increasing in a number of industries from food and beverage, medical and marine to integrated circuit manufacturers.

Ensuring the best solution
While it is important for an insert manufacturer’s technical support team to review each design, they should also have the ability to read, write and modify CAD files and isometric drawings. Some manufacturers, like Tri-Star for example, also include downloadable CAD information from their website for most standard, catalogue items. This allows engineers to visualise and validate their design concepts with the inserts they are considering using in their application.

Edelson adds that surprisingly often an inquiry from him intending to confirm the specifications of an insert can lead a distributor or OEM/moulder to a breakthrough in quality or service life.

“The teamwork among the engineering staff of the OEM customer and technical services/design staff of the insert manufacturer can create a type of synergy that results in superior product performance as well as cost and downtime savings,” Edelson says. “It also demonstrates that these profitable outcomes offer conclusive proof that the customer doesn’t need to try and go it alone.”

Claire Aldridge Deputy Editor t: +44 (0) 1727 814 450

Having joined the magazine in 2012, Claire developed her knowledge of the industry through the numerous company visits, exhibitions and conferences she attended both in the UK and abroad.

Claire prides herself on keeping readers well informed and up to date with the latest industry news.