What Experts in the Rotational Molding Industry Expect from Designers? Part 1

I’ve written many articles for RotoWorld® during the past 11 years pertaining to design and they have all had one thing in common other than some design, related topic. They all were based on my opinions and perceptions. I’ve often wondered what others in the industry thought about design, designers and preferred design skills, which provoked me to write a feature article on this subject. I therefore set out to interview leaders in the industry during ARM’s last annual meeting held in Denver in 2015. My selection of individuals whom I recorded was intentionally broad based so I could gather a wide perspective of opinions originating from different sections of the industry. This article, Part I of a two-part series, represents their opinions based on interviews I conducted in a casual unscripted format. I hope these impressions and opinions will stimulate further discussions pertaining to design, leading to improvements in the industry.

Interview with Glenn Beall
The Wizard of Rotational Molding Design

Question – What essential skills and knowledge should a designer possess to properly design a rotationally molded product?

Glenn  – A designer should have a basic overall knowledge of the industry. He or she should go to a hardware store and look at examples of rotationally molded parts to get a sense of what they look like and how they are molded. They should attend conferences and should read as much as they can about the subject. Unfortunately, there isn’t as much published about rotational molding as there is with the other plastic molding processes. I do admit it is difficult to get sufficient information about designing rotationally molded parts. There aren’t too many classes or articles written about the subject. In my opinion the basic problem with designers who attempt to design a rotationally molded part is the fact that they have no prior experience or knowledge about the process. All too frequently they do not take the time to gain that knowledge. There are parts being submitted for rotational molding that have been designed for injection molding or blow molding.

Question – Do you think that many people often confuse the activity of generating CAD files with part design?

Glenn  – Yes, I agree that most people have no idea what knowledge and time is required to invest in a well thought out, well-designed rotational molded product. This is why it is so difficult to get appropriately compensated. People think that any draftsman can easily churn out two to three CAD models in a day. They don’t consider parameters like FDA regulations, environmental factors and material selection.

Question – As a highly sought after expert witness, do you believe companies manufacturing rotationally molded parts conduct sufficient testing and evaluation prior to releasing a product into
the marketplace?

Glenn – It depends on the size and level of sophistication of the OEM. In the early days, companies often made prototype molds and tested the product. Today, there are simulation programs and pressures from management to try to bypass testing due to scheduling pressures or cost constraints.

Question – If you were offered a project which you believed required testing for reliable, safe performance but the OEM stipulated that there would be no testing or evaluation prior to manufacturing, would you accept the project?

Glenn – I have either declined these types of projects or accepted them on the condition the OEM included a written “hold harmless” amendment in my contract. There are many highly intelligent, well educated people in business today who state they don’t have time for a prototype despite the fact that the product is dangerous and warrants extensive safety testing. They are under the assumption that first production shots with today’s technology will be perfect. This may be true as far as parts fitting together, but not necessarily in regards to performance and long term safety.

Question – What are the most commonly overlooked design parameters in rotational molding?

Glenn – It starts with the molding sales reps who accept virtually any application by over promising their perspective customers that they can do anything. Today molders are afraid to inform their customers that something can’t be done. They try to accommodate the designer’s expectations of attaining unrealistic tolerances or molded features so as to not inconvenience him with added work. This information is conveyed to the technical staff at the molding facility which is discouraged from making any changes or providing suggestions to the designer that might jeopardize the sale. In addition to the sales pressures, molders are reluctant to suggest any design improvements, which could potentially increase their liability by altering the design. Rotational molders also have a habit of not paying attention to details when they release drawings to tool makers. They should sit down with the mold maker and discuss important product details, where the parting lines will be located and how the mold will be run; either stand alone on a single arm or ganged up on multi-arms.

Question – Where does a designer’s responsibility end and rotational molders responsibility begin?

Glenn – A molder’s responsibility begins when he starts talking to a designer, but legally it begins when he accepts an order.
It has been proven in court many times that the molder is the one entity in the entire chain of contributors within any project that has enough overall knowledge to be able to manage the final outcome of the project or product. The molder is knowledgeable and experienced in specifying the tooling, knowing how a material will mold and how to apply molded in graphics. A designer is responsible for developing a structure that will perform as required within cost constraints based on a specific material and selection of a manufacturing process.

Question – Should a designer specify a specific material or leave it up to the molder?

Glenn – The molder should never specify a material. He may recommend two or three different materials for the OEM’s consideration. More specifically, a product designer is not an expert in materials, tooling or molding and is typically not knowledgeable enough to make decisions within these different areas of expertise. He is responsible for recommending a molder who has a comprehensive overview of the entire chain of events starting from the concept and ending with production runs. A molder typically knows the limitations of different tooling methods as well as which resins are best suited to a given product and his manufacturing operation. He is essentially the project integrator responsible for bringing all the parameters of the project together, resulting in a manufacturable molded part.

Question – Should a designer know the design limitations inherent in the different tooling options afforded by rotational molding, i.e. sheet metal molds vs. cast aluminum vs. machined molds? 

Glenn – No, a designer doesn’t necessarily have to know these distinctions between mold types. All he has to do is review his drawings with a molder who can advise him with what can be achieved with different tooling technologies.

Question – Do you think that a designer should develop a document with a comprehensive set of specifications before
he or she attempts to actually begin design activities?

Glenn – It doesn’t matter what you’re designing, whether it’s a sheet metal part or a rotationally molded part, you should always define what is required for the product. You should collect all that is required by that product to perform its function and document it. After this is done, you can begin designing a product to address those requirements. You begin developing concepts with sketches which are shared with other individuals responsible for the product. The sketches are then modified and refined through a series of iterative improvements. It’s really important to develop a solid concept from which all subsequent design steps will follow. These steps eventually include process and material recommendations and all the details associated with those decisions. Typically you should select the material first then select the process because all processes can’t necessarily mold every material.

Question – How would you describe the differences between an independent design consultant, an OEM designer and an in-house designer working for a custom molder?

Glenn – An independent consultant designer is typically a generalist with a broad knowledge of applications, the capability of different materials and manufacturing processes. He must have a broad knowledge base to be effective as a consultant. An OEM based designer on the other hand typically has a much narrower knowledge base with a concentrated focus on the particular product line. A captive designer employed by a molding company usually has the most comprehensive knowledge of the materials, tools and processing capabilities of that molder. He/she may not have the knowledge of the product or application being considered. However if you combine an in-house designer working for a molder with an OEM designer, you get a synergy of talents and the best chance of success.

Question – Based on all your years of experience in the rotational molding industry, what percent of rotationally molded products do you think were designed with a comprehensive knowledge of the application specifications, materials, tooling and process requirements? 

Glenn – I can’t give you an accurate percentage, but I can state that rotationally molded product designs are typically much less comprehensive in addressing these parameters than injection molded parts. This is primarily because rotational molding is not as common as injection. It has not been subjected to the same in depth analysis as injection molding. This has resulted in a general lower level of experience for designers involved with the process.

Question – What do you think is the biggest problem in the design community today when it comes to proficiently designing plastic parts?

Glenn– The biggest problem is lack of education about designing with plastics in colleges and universities. Over two hundred institutions teach engineers about mechanical design but less than two dozen teach their students anything about plastics. When these graduates enter the work force they’re not interested in reading about how to design plastic parts and they are ill prepared. Many older, highly experienced designers in the plastics field are less likely to be available as mentors to younger designers because of corporate cutbacks, thus increasing the knowledge gap.

Question – What traits do you think are essential for a great designer?

Glenn- I think great designers should be creative; they should have strong personalities and strong convictions. Most of the really good designers I’ve met have been smart as well as responsive to suggestions made by others involved in a project. Another trait great designers possess is being inquisitive. They are always interested in new ideas, information and knowledge. I think really great designers are not reluctant to pick up and feel a part, examine it, ask questions, and try to gain a deeper understanding what went into the design. Designers who truly distinguish themselves never settle for the first idea they come up with, they tend to explore many options before selecting the ideal solution. They may develop three, four or five ideas before narrowing down their selection to the best design solution.

Question – As a highly respected and admired designer in the plastics industry, do you get stimulated when you are actively brainstorming with others during the development process?

Glenn – Yes, absolutely. I get extremely stimulated when I engage with others to develop concepts and potential design solutions. There have been many occasions throughout my
career when I have found exchanging ideas amongst a small group of creative individuals to be personally satisfying as well as extremely beneficial to the program.

Interview with Steve Osborn
President of Trilogy Plastics

Question – Do you have designers on staff?

Steve – No, our ISO classification does not allow us to provide design, but we do provide support to our customers with manufacturing engineering support.

Question – Are most of the designers you work with employed by parent companies or are they associated with independent design firms? How familiar are these designers with the rotational molding process?

Steve – We are a tier one supplier with large billion dollar companies who have in-house design capabilities with experience in designing rotationally molded parts. Typically these companies are staffed with experienced designers who teach new hires about rotationally molded part design, thus sustaining a continuous stream of experienced designers. They often get us involved in the design process at the early stages of design, which essentially established us as a partner. This also insures the parts are moldable and easily manufactured.

Question – Aren’t you concerned that your customers will send their files to your competitors for competitive bids after you have invested all that time in assisting them to get the design ready for production?

Steve – Some of our customers distribute files for competitive bidding, but I would rather have a part that we can make and competitively bid than a part we cannot make and competitively bid.

Question – Do you find yourself at an advantage because you helped them design the parts?

Steve – Always, because they know we understand the product requirements and that we can make it.

Question – What is the most challenging requirement designers expect from you?

Steve – Maintaining their tolerances. We often try to convince them to increase clearances to comply with the size variations inherent in the process.

Question – Do you also advise your customers to delay ordering large inventories of parts that are to be assembled within a product until you have a chance to mold a few samples to check the actual production dimensions? 

Steve – Yes, we find that the commercial tolerances of
+/-.010” in/in are really not what you are going to mold your parts at if you have your process under control. You run parts first to see how they will shrink, then you can run production with much tighter tolerances.

Question – After you have optimized your processing parameters what have you found to be the actual repeatable tolerance you can attain during production?

Steve – We can expect to maintain +/-.005 in/in. for specific critical dimensions. We can’t necessarily attain this for all dimensions, but we can maintain these for specific critical dimensions.

Question – How do you address your customers who require stringent aesthetic standards to be maintained?

Steve – Since most of the products we mold require high aesthetic standards, we are accustomed to carefully handling parts. Parts are not thrown or roughly handled to avoid scratching or distortion.

Question – Do most designers you work with understand draft angles, parting lines and how shut-offs in molds affect part design?

Steve – Most of the designers we work with have a basic understanding of draft angles. We typically advise them to locate their parting lines on a bead or locate them in areas that are not prominently visible. Our advice to designers who wish to include a shut-off or by-pass in their design is simple. The greater the shut-off angle, the longer the mold will last without some sort of maintenance rework. This is a trade off with our customers.

Question – Are most of the designers you work with industrial designers or mechanical engineers?

Steve – Most of the designers are mechanical engineers. However, we find the best designs are coming from industrial designers working with mechanical engineers in tandem. These parts are typically aesthetically and mechanically optimized.

Question – Do you find it necessary for designers to have a comprehensive understanding of the rotational molding process?

Steve – Although designers with some practical experience are much better, we typically provide technical input, which is why we want to get involved really early in the development cycle. We’ve discovered that our early support helps us gain the confidence of our customers to mold their products to their specifications. For example, we find that our suggestions pertaining to secondary operations help our customers as well as our ability to cost effectively manufacture the product.

Question – Do most designers you work with have a good understanding of materials and properties?

Steve – No, they simply state high or low density polyethylene without much understanding of the differences in these materials. We have one customer who expected their product to perform at 125 °F temperatures under load and they have experienced excessive distortion which has resulted in mold revisions. Larger companies routinely perform FEA studies, but most companies don’t inform us of all the specifications or they change the specs. We typically inform companies of what is possible as well as not possible. Most designers have unrealistic expectations which must be revised for the real world.

I’d like to thank Glenn and Steve for sharing their insights and perspectives about design with me and the readership of RotoWorld®. I’ve learned a great deal speaking with these two highly accomplished individuals and hope all of you have been equally enlightened as well. There will be a continuation of these interviews in the next issue of RotoWorld® with other industry leaders. The next issue will include individuals involved with tool making, equipment, processing and design. Please send me your comments about this article, I am always interested in receiving your opinions to improve the content.

from an article at RotoWorld®
https://rotoworldmag.com/what-experts-in-the-rotational-molding-industry-expect-from-designers-part-1/