This technical information has been contributed by
SPI Industries

Blow Molding Gets a Second Look for Parts with Complex Geometry

Blow Molding

Traditionally seen as a process for making plastic bottles and containers, blow molding can be used to make a variety of thin-walled, structurally-sound hollow parts out of engineered plastics

Blow molding is most often used to produce strong, hollow containers with simple shapes, in sizes ranging from small beverage bottles to relatively large fuel tanks, drums, and trash cans. But SPI Industries, a South Bend, Indiana-based custom injection molder that also operates a blow molding plant in Coloma, Michigan, has unleashed the capabilities of the process in ways that many design engineers never thought were possible. At a recent Design-2-Part Show, SPI Industries exhibited a variety of blow molded parts, many with complex geometries, for applications not typically associated with blow molding.

"Blow molding works in a lot of different geometries," SPI Industries President John Doster told Design-2-Part Magazine in a phone interview. "We make parts that a lot of design engineers wouldn't think about making using blow molding."

SPI Industries ( got into blow molding in 2008, when it bought the blow molding operations of Modern Plastics Corp. in Coloma, Michigan. Long a respected name in extrusion blow molding, Modern Plastics had been in business since 1937. Today, SPI is picking up where Modern Plastics left off, working with engineered plastics to produce structural parts with high strength and complexity.

"We like to produce the challenging, difficult parts," said SPI Industries Director of Marketing Don Patzer. "This is where we got our reputation, taking ideas that are off the beaten path and bringing them to fruition."

In a recent phone interview, John Doster, Don Patzer, and Vice President and General Manager Ed Trapp talked about the advantages of blow molding and how SPI Industries applies this specialized form of molding to complex parts. A transcript of their conversation with D2P's David Gaines follows.

D2P: SPI Industries has long been known for its custom injection molding services. What prompted the company to get into blow molding, and can you tell us a little bit about the company's predecessor in blow molding, Modern Plastics?

John Doster (JD): SPI Industries has a long-term relationship with Modern Plastics. We were using them to injection mold certain parts on an overflow basis. When the liquidation news came down about Modern Plastics, SPI was notified within a matter of hours. SPI knew that it could not save the larger injection molding operation, but was confident that it could step in and keep the blow molding operation stable.

SPI was aware of the historical reputation of the blow molding plant, and felt that with the proper financial strength behind it, the return to prominence would just be a matter of time. We were in a unique position, to be able to react quickly on the decision to purchase the blow molding operation, because of the relationship we had with Modern Plastics. The bank only had two weeks to get everything wrapped up.

Number one, SPI was motivated to save jobs here in Michigan, and, at the same time, to expand the molding capability of our company. We have about 17 employees at the plant right now, and we employ about 50 people at our injection molding operation in South Bend, Indiana.

Don Patzer (DP): Modern Plastics started in 1937 as an injection molder, and, in 1961, made a decision to build a plant to accommodate the blow molding process. Our achievement was that we were in a joint development program with General Electric in the early '80s to develop structurally-engineered plastics. Through that relationship, as a joint venture, we helped develop the GE Noryl® resins. Borg Warner was also involved with their engineered resins. So we kind of set the stage for structural plastics within the blow molding industry. In '84 and '85, we got involved in a joint program with Xerox Corp. in Webster, New York, to design structural plastic parts for their copy machines.

D2P: Can you talk about some of the complex-geometry parts that SPI is able to manufacture for applications not typically associated with blow molding?

DP: Normally, blow molding is associated with plastic bottles and containers. There are only a handful of companies in the country that are capable of producing the complex geometries that we do. We were a pioneer in this field; we got our start making Playskool's little toy tool sets and wheels for wagons. Once we got into the engineered resins, we were able to design thin-walled hollow parts and flat panels for Xerox copy machines. This led to a partnership with Kodak in Rochester, New York, to make fluid management systems that went into their paper and film machines.

Following those types of applications, we developed head and foot boards for hospital beds, and some underlying bed structures and CPR boards. Again, a lot of these are thin-walled, hollow parts, but structurally sound. The complex geometries that we blow molded then--and currently mold--are not typical of standard, everyday blow molding.

JD: You could say the company was certainly one of the pioneers leading this structural blow molded technology. We first started to produce parts for Xerox in 1984.

Ed Trapp (ET): Previous to that, we had made a few engineered parts out of low-density and high-density polyethylene and polypropylene, and a little bit of ABS. When we started working with GE, they brought in about eight to ten grades of Noryl®. We were able to mold parts in every grade that they brought to us. At that point, they critiqued the parts as we worked on them, and then improved on them to make the materials they have today. (Noryl® is a modified Polyphenylene Oxide developed by GE Plastics in 1966.)

Prior to that, we made some parts that went into outer space as food containers. We manufactured drying equipment parts, which blow molders typically didn't get into when the preferred resin was polycarbonate. We had equipment that allowed us to get into designing screw geometries that allowed us to run the difficult engineering resins. We even did a lot prototype work for Dow for their automotive and other applications. I think that the work that we did not only helped us, but helped the rest of the industry become what it is today.

D2P: How is the company able to use blow molding to manufacture parts that many people wouldn't consider feasible through blow molding? What enables you to do this?

ET: We can take a look at an engineer's concept and critique it. If it's blow moldable, we will fine tune it. We try to get involved as early as possible to look at what they're trying to do, what the part is used for, and if there are any ways we can add to it. Sometimes, we can eliminate components for them, and we can give them features that they didn't realize were possible. As far as SPI is concerned, we will look at any material that a part can be molded in. A lot of blow molders don't like to work with engineered materials, but there aren't any engineered materials that we turn away. And we don't mind very low volumes, and working with multiple grades of material in one project. So I think being versatile is one of our strong points.

DP: We like to produce the challenging, difficult parts. This is where we got our reputation, taking ideas that are off the beaten path and bringing them to fruition.

D2P: What benefits, in terms of cost and quality, is SPI able to provide its customers by blow molding these parts? In other words, what's the value of using blow molding for these applications?

JD: The benefits are being able to make a plastic part of such complex shape and strength that may have been overlooked by design engineers in the past.

ET: Surprisingly, a lot of design engineers are not too familiar with blow molding. I always made the assumption over the past few years that this notion was going away, and they were becoming more familiar. But it's evident from the last couple of tradeshows that we've done, from the amount of people that come in and are surprised that the parts we display are blow molded. There's a lot of education that has to be done.

D2P: What specific blow molding processes--extrusion, injection, or stretch blow molding--does SPI offer?

ET: We offer extrusion blow molding. Usually, the other two processes are for very high volumes in the container industry. Companies usually use injection and stretch blow molding for quantities in the hundreds of thousands. Extrusion blow molding is usually concerned with the functionality of parts and the complex geometries that the other two processes can't really touch.

D2P: Can you talk a little about the advantages of the extrusion blow molding process?

ET: We can get into some very large parts. We have equipment capabilities up to a 40-pound shot. But I know that the industry can go way beyond that shot size. We sometimes provide large table tops and cabinet tops that are 50 inches x 30 inches, so we can make large structural parts. We also manufacture parts for fluid and air management, where they need multiple ports in a container; those are a challenge for us.

D2P: What makes a part a good candidate or a bad candidate for extrusion blow molding?

ET: A good candidate is when you can give somebody everything they're looking for and then some. Blow molding is not good for something with large, square corners, so a bad candidate is something like a large, square container, maybe 4 feet x 4 feet. Basically, if a part will work with a single wall, then injection molding is the way to go. If you're making a tube that has to have a bend in it, and you can't pull any cores on it, then blow molding makes sense. Basically, it has to do with the geometry of the part, and what you're trying to achieve.

D2P: Your website says that the company has both types of blow molding presses--reciprocating and accumulator. What are the differences in the parts that these presses produce, and what determines what type of part goes on which press?

JD: In our plant, we will typically use the reciprocating presses for the smaller parts, and the accumulators for the larger parts. This has to do with how the parison is formed; it also has to do with how the material is stored prior to the shot.

ET: You can, however, make both types of parts, small and large, on both machines. Typically, the accumulator head is used to extrude the material inside the machine until you get to the desired shot, then the hydraulic cylinder will push it out to form the parison that you need. A reciprocating screw works a lot like an injection molding press. The screw runs backward to accumulate the material in front of it, and then pushes forward to shove the material out and form it into a cylindrical tube of plastic that will be extruded out of the die.

D2P: What processes do you use to make prototypes for injection- and blow-molded parts?

JD: For injection molded prototypes, we will typically use an SLA prototype.

ET: If the blow molded part will eventually go into production, we will make low-cost tooling to form the part. In blow molding, if you want to get the physical properties of the part, you almost have to mold it the way it will be processed during production. So you can make inexpensive aluminum tooling to start with, and probably not put as much venting and water lines in it.

D2P: Your website states that SPI offers low-cost tooling and low-cost production for its molding processes. How is the company able to achieve these customer benefits in today's economic climate?

JD: What we were talking about on the website is family insert molding, which means, for example, that you can have a twelve-cavity base and have different parts running in each cavity. This is a different process than inserting metal parts into the mold in injection molding. Therefore, each of the cavities can be interchangeable very quickly, and we can make twelve different parts at the same time.

So in effect, for a customer that may want to get multiple-cavity pricing, we would simply make a very small cavity and run it along with other parts. This would give them multiple-cavity pricing for production, but they would only have to buy tooling for one cavity. The downside to the family insert molding is that all the parts in that base have to be made of the same material with the same color. At the current time, we mostly use Nylon and Acetal® for this process. For instance, small rollers, slides, and screws can all run together, if they are made out of Acetal® or Nylon.

D2P: SPI Industries is said to have evolved from an ordinary molder to a fully-integrated contract manufacturer. How did this happen, and what makes you fully integrated?

JD: What we're doing is taking on as much of the responsibility for the manufacturing as possible. An example would be from three of our best customers who are now really virtual manufacturers. In other words, they do the selling and market development, and we do the engineering, manufacturing, warehousing, fulfillment, and shipping to their customers. We also have engineers on staff, and so for several of our customers, we also handle the engineering function. We can handle product development, tooling design, right on through to the final steps of production and shipping. So we really are a fully-integrated shop.

D2P: The global marketplace is now a reality for every American contract manufacturer. How is your company fitting into this 21st Century reality?

DP: Both of our divisions--injection molding and blow molding--supply to other countries offshore, such as Mexico, Canada, Taiwan, and countries in Europe. Another side note is that we also have the capability, if the customer requires it, to source tooling and other customer requests offshore. We buy and sell globally. Buying tooling overseas is usually at the customer's request. We prefer to shop locally, and we prefer other folks to shop locally, too. We purchase most of our tooling from domestic suppliers, since we don't make most of our tooling in-house. And we supply small, thin-walled parts to Japan.

D2P: Have any of your customers brought their manufacturing back to the U.S. after having gone overseas?

JD: The answer is yes. One of our customers has a molding operation in China, and is now using SPI for mold design and building very small, thin-walled electronic sockets that require low volume and high precision. It's the low volume and high precision that brought the company back to the United States. Freight costs weren't an issue, but rather making precision parts in small volumes. It's hard to turn a machine on and make perfect parts immediately, but once you've made 100,000 parts, you're probably going to make good parts. But if you're asked to make 2,000 parts, it might take 1,000 or more parts just to make the first good one. It's not something that works very well in China.

DP: As a side note, what I've heard in the marketplace is that because of the growing Chinese economy, a lot of what they're producing now is to satisfy their own domestic needs. Therefore, a lot of Chinese manufacturers don't have the time to do our work. This is especially true in their automotive industry.

D2P: What reasons did they give you for coming back?

JD: The smaller volumes don't meet the Chinese manufacturing model. They don't want to deal with American companies that want small volumes.

D2P: If a potential customer is considering going offshore for manufacturing, what would you tell them about SPI's services that would make them reconsider taking work overseas?

JD: What we would do is emphasize the obvious. Number one, larger parts cost more to ship and will continue to become even more costly. Number two, quantities will need to be greater when you're purchasing offshore. Number three, long lead times and forecasting accuracy are absolutely critical for overseas manufacturing, especially because in today's economy, it's very hard to forecast accurately. Number four, and probably the most important one, fast response to solve customer issues is very difficult, and is extremely expensive when the manufacturer is halfway around the world.

Timing is also very tough, so it's very hard to put out a fire. For example, you might be used to getting 10,000 parts at a time, and something goes wrong and you only need 1,000 parts. Domestically, you can get the 1,000 parts in a couple of days, but you can't get them from an overseas supplier in a couple of days.


Delrin is a registered trademark of DuPont.

This technical information has been contributed by
SPI Industries

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