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Written by Per Flem, President of Recto Molded Products

About Written by Per Flem, President of Recto Molded Products

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The Four Types of Robotics That Are Commonly Used in Injection Molding

The very first experience I had with robotics was back in the mid-1980s when I purchased a used Sadamel vertical press from Switzerland. It was a high-precision press designed for watchmakers. Its pneumatic picker removed parts and runners from a vertical clamp at high speed. It made vertical presses relevant again for high-speed molding. Molded-in inserts wouldn’t fall out when the clamp closed.

As with most choices in life, there are reasons you take one path when there are many to consider–and the same applies to the integration of robotics into a plastic molding company. Robotics has many applications in the industry, and the type that you choose depends upon what you want to do, how much you can spend, and how much flexibility you want. The four main types that are applicable to injection molding are described in this article, with pricing based on the use of 250-ton presses.

Sprue Pickers

Sprue pickers are the least expensive, ranging from $5,000 to $10,000, and the simplest of the four types. They are most cost-effective for basic needs, such as taking a runner and putting it into a grinder, or putting edge gated parts in a tall drum to be gated the next day. You can take this motion and remove runners from a three-plate mold or knock the runner on that mold out from between the plates. Beyond these activities, the sprue picker is limited by its three-axis capability and isn’t as flexible as other types of robotics. 

Sprue pickers are excellent for molders just getting into robotics, as well as molders running two-plate, sub-gated tools. The machines travel down into the mold, grab the sprue/part, pull away from the parting line, retract to the start point, rotate away from the molding area, extend to drop the runner/part into a grinder or receptacle, return to the home position, then rotate to the start position. A flex option on the grippers adds a fourth axis to help get a large runner into a grinder. 

This type is mounted to the stationary platen on the molding machine. Sprue pickers are typically pneumatic devices, but more expensive servo versions can be purchased for greater flexibility.

Spruce Picker

Traversing Robots

Traversing robots are mounted to the stationary platen and have a traversing motion instead of a rotation. Typically, these are servo-driven, although there have been versions with pneumatic operation on the extract axis. Because they are often servo-motor driven, there are some limited secondary operations that they can perform, such as delegating, stacking, and filling boxes. When you add fixturing, traversing robots can load inserts and labels as well. Safety cages are necessary for traversing robots, but are much smaller than those required for six-axis robots since most of the work occurs high in the air.

Traversing robots can be used to remove large parts from a press and put them on a chute or conveyor belt. They also can perform special handling of parts that require secondary operations such as drilling, or assembly onto another hot part, where you can shrink-fit onto a cold part like a ball bearing. If the hot plastic part were to be put into the inner race of the ball bearing, it would shrink away and become loose.

The cost of an average traversing robot is $30,000-$45,000.

Traversing Robot

Side Entry Robotics 

These high-speed robots are typically used for installing labels into a cavity or on a core, removing the part from the press, and stacking or loading parts outside of the media in bags or boxes. With total cycle times of 2-3 seconds, they are amazing to watch with parts staking up quickly–but they are the least flexible type of robot and tend to be the most expensive. They require space around the press and are the most challenging to program and operate in order to achieve the greatest output.

Side Entry Robot

Six-Axis Robots 

Six-axis robots are the most widely seen on TV and the internet, welding or moving automotive body parts. Though more expensive than other types, six-axis robots are the most flexible and precise option, and they can be rebuilt after hundreds of hours of operation and start life anew without compromise, even if the robots are decades old. 

A new Fanuc six-axis robot typically costs $40,000 to $50,000, but a rebuilt unit costs just $25,000 to $35,000. They tend to take up more room than traversing robots, because six-axis robots are typically mounted on a pedestal outside of the molding area, while smaller versions can go on the stationary platen and take up far less space. 

Because they have so much flexibility, programming is a more critical factor for six-axis robots. From removing runners to loading metal inserts, delegating parts, loading parts onto a conveyor, and putting parts into cartons, providing a step in an automation process where the orientation of the molded part can become very costly in a separate cell, the flexibility is dramatic–but programming and robotics experience is vital.

Six-Axis Robot
Six-Axis Robot

The benefits of integrating robotics into an injection molding shop

The use of robotics has many advantages in the injection molding industry. Their use results in fewer rejects and better efficiency. Grinders are less likely to get clogged and the robotics equipment can perform its tasks reliably and consistently. With skilled and experienced employees, robotics are excellent for large parts or long-runs of production, starting with production runs as small as 1,000 parts. 

About Recto Molded Products

Recto Molded Products has well over a century of experience in injection molding, and is well known for its extensive use of robotics and automation throughout our plastic molding company. Check out our website to learn more about us and to request a quote.

Getting the lowest price for injection molded parts, without sacrificing quality.

Think like a molder 

All customers want the lowest price possible, so how do you get it? You think like a molder and address the concerns that affect pricing.

What is the price the customer is seeking? Target pricing is a goal/challenge that is a good first step. The molder then considers what is it going to take to make that happen, rather than what do we guess the customer wants. A goal if you will.

Am I getting all of the information I need? How well does the customer communicate their specific needs?  Are cosmetic requirements, reasonable tolerances, and other specifications appropriate for end use, and in what environment?

Consider the redesign

How much redesign will it take to achieve the goals? Will I have access to engineering to answer questions regarding quality issues, material selection, and cost reduction programs? Are there budgets available for testing alternative materials? This aspect of arriving at pricing goals is generally overlooked. When an engineer specifies a material it is often because of a few parameters. First no one wants failure during the life of the product, so the inclination is to over specify from a viewpoint of what has been working on similar applications. 

Choosing certain materials can lower the price of your parts

Thick walls add cost!

When the quantities are modest, long-term testing probably is less cost effective than jumping up from, say, a polypropylene to a nylon with a little bit of cost increase. Long term testing might show polypropylene would work just fine, but testing cost would be prohibitive, and lead times increase. When the molder uses larger quantities of nylon, and would need to pay a premium for low quantities of polypropylene, the answer gets muddier.

Is the customer receptive to looking at materials currently being used on a daily basis to keep prices and deliveries controllable?

Are there expensive brass inserts in the design? Can they be replaced with inexpensive square nuts?

Wall thickness is a factor

The common method of looking at a part as a machining operation is just the reverse from designing as a molded part. The first method is removing material from a solid block, the other is defining the working surfaces and supporting them with structural features. When wall thickness is kept identical, the differential shrinkage due to different walls  and accompanying warpage is minimized. When walls are too thick, higher pressures are needed to keep the part void free, resulting in greater stress. When walls on a single part are both thin and thick all kinds of problems can surface. This is why molders always ask for coring: thicker walls always add cost. Both material cost and processing cost (longer cycles for cooling). Sometimes the reason for a thicker wall is stiffness, which is true but can be also achieved by using stiffening ribs or walls, or with glass fiber in the resin. 

Sometimes the thicker walls are perceived for impact strength, which isn’t always the case. Consider a thin wall soda bottle, versus a thick wall bottle of the same design. The thin wall will flex rather than break; clearly elongation is the important consideration. I once heard from the manufacturer of Ultem that a wall of greater than 3/16” with 30% glass filled Ultem would not be beneficial in any way to part design. It would be more expensive, it would not have better impact strength, or if properly designed, be any stronger. I believe this is a good general statement for any molded part. Requiring that thickness causes voids to develop, stresses get higher, and cost climbs with material cost and processing times.

How to add value to the initial part design being quoted 

Thin-walled part with ribs to achieve impact strength with stiffness.

When the design seems complete, can we integrate other attached components into the part? How about other “free” features such as part number, or instructions for example ”uses 10-32 bolt”. Can assembly be made easier by longer lead ins on the holes for screws? Have we included radii to all inside corners to improve impact strength, and reduce stress risers?

What will the working relationship be with the QC department? Do they react appropriately to the issues? When a shipment of 100,000 parts uncovers one “short shot”, will the molder have to spend hours with a returned part, root cause analysis, paperwork that is often inadequate in the eyes of the QC representative, and a fine as punishment? A symbiotic relationship works much better.

Don’t forget the packaging

Then there is packaging: Can we use returnable or disposable packaging materials? The packaging cost for 10 large parts in a $2.50 cardboard carton  is much more expensive than one hundred in a disposable gaylord.

Can quarterly purchase orders with monthly releases work?

Has this existing customer, or will this new customer provide adequate lead times, or will every order be an emergency? How much inventory will I need to maintain to meet lead times?

How does the customer pay their invoices? 10 day payment terms always reduce costs.

Bottom line is it all comes down to understanding both parties’ needs and expectations, and how the cultures complement each other.

.50 cardboard carton  is much more expensive than one hundred in a disposable gaylord.

Can quarterly purchase orders with monthly releases work?

Has this existing customer, or will this new customer provide adequate lead times, or will every order be an emergency? How much inventory will I need to maintain to meet lead times?

How does the customer pay their invoices? 10 day payment terms always reduce costs.

Bottom line is it all comes down to understanding both parties’ needs and expectations, and how the cultures complement each other.

A Detailed Look at the Quoting Process for Plastic Injection Molding

Firsthand Advice from a Injection Molding Expert

How do molders go about determining the appropriate price for an application? 

When a molder receives a print or a solid model and production quantity, the conservative first pass or ballpark pricing will always reflect the unknowns that can–and often do–surface later down the line. The more upfront data provided to the molder, the more accurate and typically lower the upfront price. This data can include a wide range of factors such as yearly consumption, specific color requirements, special packaging, payment terms, and quality specifics. And these are just a few of the aspects that the molder will ask about. 

A case study in why having complete information is important

Perhaps the most difficult request that plastic injection molders can receive is a request for a part price on something that is currently being made through a different supplier. This could be for a simple ‘price check’, an attempt to find a new supplier, or ‘reshoring’ parts previously made offshore. 

Regardless of the reason, these types of quote requests often come with a history that the customer may not be aware of, such as:

  • The material used and how it might be colored
  • The number of cavities in the mold
  • The required cooling time
  • The type of mold steel used
  • The condition of the tooling
  • The use of edge gates or sub-gates
  • Is extended cooling time required due to inadequate ejection
  • The potential for dimensional or warpage issues

And the list goes on. 

Bringing as much information as possible is important for an accurate initial price. However, the molder will always have questions, and answering them as thoroughly as possible will give them the information that they need. Bringing sample parts can be a large benefit, as well as any information on the mold itself and its design, such as the knockout pins, parting lines, gates, cavities, and more. 

What happens with a preliminary design?

The other type of quote request that molders typically get is for a preliminary design for a component, often including a 3D model of the part as well. Other information should be included as well, such as the function of the part, the environment that it will need to withstand, assembly concerns, and any cosmetics required. The more the molder knows about the entire product, the more successful the project will be.

With a new design to quote, design questions regarding draft angles, cosmetic surfaces, loads, temperatures, colors, assembly techniques, location and quantity of ejectors, gates, parting lines, areas where warpage may occur (flatness), the use of threads versus self-tapping screws, molded in place metal inserts, thick walls, and sink are all considered. Features such as undercuts, which can be designed out of the part, reduce tooling costs.

Who chooses the materials?

Material decisions are typically made in collaboration between the molder and the customer, but they depend heavily on the experience of the injection molder. Molders prefer materials that they can source in large quantities at reasonable costs, with many inventory turns per year–and their customers benefit from the molder’s expertise, getting lower prices and faster deliveries. 

As an example, the short-run part that needs 50 pounds of a specific material a year and can only be purchased from the requested source in 2,000-pound minimum quantities is not a good fit with pricing and long-term inventory issues. 

Having a molder with extensive material application knowledge is invaluable in all cases.

Who chooses the tooling?

Experienced molders will typically source the tooling for a project, based on the parts that they make and their own personal preferences. For instance, Aluminum tooling is less expensive but doesn’t last as long as fully hardened tool steel. At Recto, we avoid aluminum molds and typically use hardened steel or a similar material. Some molders use them exclusively. Aluminum molds running 30% glass-filled polymers don’t last long, while the same molds running polyethylene can function very long with little to no damage to the cavity. 

When a customer starts the conversation with the statement, “We will only need 100 parts, ” aluminum must be considered, as it’s a cheap material that will last long enough for the run. However, aluminum isn’t a feasible choice for large production runs of thousands to tens of thousands of components. In such cases, hardened steel molds are the more cost efficient choice, despite being more expensive upfront. 

A case study in material selection and experience

The more experienced the quoter has become, the more questions are asked, and experience is a great educator. Many mistakes/missteps have made the quoter wary of missing information, which has a significant effect later. 

A good example was an application for a coffee vending machine, a solenoid dispensing valve. Requirements were for boiling water, chemical resistivity for coffee, cleaning agents, and suitable long-term seal surfaces. CPVC was initially chosen, but before the ink was dry on the tooling purchase order, a change to Polysulfone was requested. 

A material supplier had convinced the customer that the CPVC was not the correct choice, but their material was better. The molder, who was inexperienced, agreed to the change on the conditions that the material supplier had to have technical responsibility from tool design to initial samples and testing. 

Six months later, and two production shipments later, the customer reported that the parts were cracking during assembly. When the molder went to investigate the issue, they discovered that the assembly operation was taking place next to the floor’s solvent welding operation. Polysulfone, the material requested by the customer, is susceptible to solvent attack. The solvent operation was moved, but the customer never used Polysulfone again. 

The moral of the story is this–not all material selections should be made from data sheets. Tensile strength is not an indicator of impact strength as much as good elongation values, and high modulus with low elongation is only sometimes a stronger part. Not until the material is brought into real world conditions does it truly prove its worth.

Conclusion

The quoting process of any plastic injection molding project often has an extensive impact on the quality of the overall relationship between the company and the customer. Not until the customer says that the molder has done their job and done it well, has the molder earned their customers’ trust.

Choosing the Right Molding Company

One size does not fit all. A customer in a highly regulated environment will need a similar injection molding vendor familiar with, and able to comply with the various certifications. There are developing requirements in some industries to “go green” which is a challenge in general for some plastics processors, but not impossible. After these initial requirements are satisfied it becomes easier to source.

In the general molding categories, all will state that price, delivery, and quality are paramount requirements. But even in these simple aspects, there are other considerations.

Price. Fundamental until other aspects are considered. Can quality or delivery be compromised? Is price a function of equipment, or people? The simplest vendor would be one person, responsible for all aspects, with no chance for communication errors. When the size of the molder increases, so do the complexity and possibilities of error. That is why standards of documentation such as ISO are important to the largest molders. But even ISO doesn’t protect all shareholders from the weakest link, it just reduces the opportunity for error in theory. A company heavy with documentation, and redundant communication channels will naturally have higher costs, and therefore higher prices. That may be important in some industries that justify the additional costs.

Service. Molders running at 80-100% capacity will not have the flexibility of rapid schedule changes. If the customer industry is a “job shop” in nature a 2-3 day turnaround to start getting parts may be critical. Some customers will value short runs as more important. Service can also mean responding to pricing requests quickly, and certainly problem-solving. It can also mean providing the technology necessary to manufacture the product that isn’t available at the customer’s disposal. Material selection, part design, and quality suggestions are all important.

Quality. Is the molder satisfied with maintaining quality that is acceptable, or do they aspire to improve as an integral part of their culture? Quality while measured in PPM, or dimensional problems is the initial consideration, however, the response to issues that develop is just as important. How quickly and thoroughly the concerns are addressed is equally important. A molder with QC people with high turnover, rather than fewer with a long job history (and memory) has to be considered. How well does management support the QC department, one of the places where fault is generally cast? Are the drawings kept current, and accurate? Does the company culture provide inspection devices that make measurements accurate and easy for off-shifts to use? Does the molder have knowledge and understanding of the component’s function to identify potential issues during production, and the life of the product?

Then there is general culture. Profitable companies typically have better (precision, speed) molding machines, dryers, robots, tool room equipment, and general hand tools. Getting better tools in the hands of employees makes them more effective, and less frustrated. While servo-electric machines are faster, more accurate, and use less energy than servo valve machines, they might not be required to handle the molding project that a less expensive machine would be capable of running. And neither machine can perform adequately if there are wear issues taking place such as a worn screw/barrel. An expensive new all-electric molding machine with wear on its screw/barrel won’t be as good as an older servo valve machine with no wear. However, when given an option, buying the more expensive, more capable all-electric machine is usually the best choice. A six-axis robot has far more capability than a three-axis traversing robot. The culture of “doing things right on a long-term basis” is a formula that will provide the required price/delivery/quality aspects, and should be foremost in selecting an injection molding partner.

Plastic News

Since 2005 Recto has initiated a practical “green” culture. Not to be confused with the current push for green at any cost, our perspective is that green can have many tints, and the one that seems the most practical is one that is simple and has appropriate payback. Not to say that we might take on a project that looks good as well as filling a need. Trees for example. The City of Cincinnati Parks Department has planted trees around our building for appearance, while the shade keeps cars cool under the shade. This cooled air also makes it into the building. We have obsoleted old molding machines for many reasons, but oil and electric consumption were the primary reasons. Along for the ride came lower maintenance, better performance and a cooler building. We got rid of air cooled chillers (160 tons), and went with water cooled chillers after replacing our old, leaky cooling tower(with twice the capacity). With the new cooling tower came a water cooled chiller, and heat pumps to cool and heat high population areas of the building. As the old leaky roof was replaced, white TPO was chosen to cool the building, increase usable life, and ease of repair. When we traded an old molding machine for a 2500 gallon water tank for rain water, we found free water, and also a cleaner cooling tower. There are fewer chemicals used to keep the buffering chemicals in suspension. We added 10,000 more gallons this year. When an addition was added, four 1” PEX tubing lines were added to the perimeter of the foundation. We use our 90 degree plant cooling water to keep the addition warmer in the winter, and reduce usage the of the cooling tower.

We use smaller compressors, located strategically located to add heat in the winter, and are located where the heat can be sent outside quickly in summer. Smaller compressors means lower startup demand and lower operating costs when variable air usage conditions exist. When air operated devices are not heavily used, only 20 horse power is running. When a lot of air is being used, 60 HP motors are used.

Like most molders that work a 5 day, 24 hour schedule, our peek electric demand soars on Monday morning startups. We have a device that monitors our energy consumption with a set of traffic lights. Red lights indicates employees to start a smaller press instead. This device also monitors power factor, showing when someone has failed to switch on a capacitor bank. Our peek demands still were a factor from 10am until 4pm as every startup and sample has begun. We added 196 solar panels to absorb that peek demand, 44kw of electricity that only provides $4,000 worth of electricity but helps cut our peek demand charges by about $7,000 per year. The solar installation was finished late 2009, and because of all the incentives (that are no longer available), paid for itself in 2 years.

In 2003 Recto had 45 molding machines. Today we have 27, all but two either servo electric, or servo pump. Servo technology hasn’t completely licked the problems with long pack times, so we keep two servo valve machines in good condition to solve that problem.

In 2003 Recto reversed it’s air quality fans so that instead of inside air being extracted in the molding area, outside air was brought into the warm molding area in the winter. Extraction fans at the opposite side of the building draws the warm air to all other parts of the building with “helper” fans in some walls to further mix the air. In the summer the fans all extract air from the building with make up air coming from the tree shaded zone around the building. Our inside air temperature is cooler than outside in the heat of the summer. This saved considerably on our heating bill. 

During this 20 year span Recto has reduced it’s electric usage in half, and it’s gas usage by 90%. That’s really green no matter how you measure it. Our building roof reflects sunlight, or trees add cooling and look good, and we collect stormwater to reduce the load slightly, at the city water treatment plant. Our employees benefit with better working conditions.