Globe Plastics would like to answer as many questions as possible in advance. In order to save you time.
- What should a mold quotation contain?
- I received four quotations and the difference in price is $30,000.00! What gives?
- I received a quote for molded parts but no tooling cost. Is the tool free?
- I received a quote and there was no tooling but there was a $10,000 charge called a NRE (or NRSU). What's that all about?
- My molder has suggested I amortize the tooling over the first year's run. Is that a good idea?
Injection Molding requires that the material be heated in a plastic state and then forced into the mold cavity under high pressures. The plastification of the material in the barrel usually is facilitated by sheer and friction from a rotating screw that also feeds in new material. In thermoplastics the material is cooled in the mold until it can be ejected. With thermosets the material is heated in the mold to "cure" the material before ejection.
Compression Molding involves a heated mold in which the material charge is placed into the mold (often having been preheated) and the mold halves compress the material into shape. Thermosets readily mold by this process.
Transfer Molding is a process largely reserved for thermosets in which (much like the injection process) preheated material is transferred with a plunger into the closed mold cavity.
Vacuum Forming begins with a thin sheet of extruded thermoplastic which is heated and formed around a core or cavity using a vacuum. Tooling can be made of wood since low pressures are used, but part design and geometry are greatly limited.
Pressure Forming can refer to many materials and processes. APP has a great range of expertise in many other molding techniques.
Tooling or Mold:
Tooling or a Mold are interchangeable terms. Before you make a part you have to build a tool (or mold) shape the parts. You will hear both terms used in the plastics industry.
Molds can be hand operated, semi-automatic or fully automatic.
Hand operated molds require an operator to physically remove the mold from the press and disassemble it to remove the molded part. They are used for very small quantities (1 - 500 parts) or parts that have undercuts, threads or other complicated features.
- They have long operating cycles (2-5 minutes or more) and by nature are labor intensive to operate.
- They are typically single cavities, inexpensive and fast to produce.
- Parts may required multiple post operations to meet design requirements
Semi-automatic molds are typically mounted in the press and require an operator only to perform a specific operation of the cycle (i.e., remove a core, place an insert, remove the part from an undercut).
- They can be very cost effective for insert molding or when quantities do not allow for the expense of core pulls, cams or unscrewing devices.
- Single or multi-cavity designs can be cost effective.
- Machine cycle times can approach that of automatic molds, but so can their cost.
Fully Automatic molds run with no operator. They may utilize a variety of mechanical devices to facilitate part removal such as mold sweeps, air blasts, sprue pickers or robots. They may contain core pulls, cams to remove undercuts, multiple plates, hot runner or insulated runner systems, unscrewing devices or any number of devices and techniques to improve efficiency.
- Depending on part design and material they can cycle extremely fast (as little as 4 seconds).
- Parts are normally finished as molded with no post operations, beyond value added operations, required.
At American Precision Products we use a variety of techniques to reduce the overall tool cost. One such measure is to use standard mold inserts. With insert molds you buy only the insert and not the mold base. The base remains the property of the molder. We use mold bases by Master Unit Die (MUD) and RoundMate© that are common throughout the industry and are readily available. The use of inserts shortens lead times and lowers costs. The drawback of mold inserts is that they are only portable from one molder to another if the new molder has the same style base. If you remove your mold from one facility it may be necessary to purchase a base.
Custom mold bases for specialized applications, such as runnerless or split cavity molds can also be used. These bases also save costs but because the are not standard to the industry the tooling is not "portable" as such. To operate the tooling at another facility a new mold base would be required to be built.
Standard mold components such as lifters, collapsing cores, accelerated ejectors as well as others also reduces engineering and construction time and thus cost.
Besides saving money and reducing lead times, the use of standard and custom bases and standard mold components allows American Precision Products to focus our attention and time on the details of the tooling that most effects your parts.
Tooling can contain one or multiple cavities (the part shape you are making). The cavities can produce the same part or different parts. If the tool makes only one part it is a single cavity tool, more than one of the same part is called a multiple cavity tool and a tool that produces a group of parts is called a family tool.
Family tools are often designated by how many cavities of each parts is produced. A tool that produces a group of parts, 1 top, 1 bottom and 2 bezels, would be described as a 1+1+2 Family tool. With a family tool all the parts can be run at the same time or, in some cases, parts may be run individually or in groupings.
The advantage of family tools is that the tooling cost is decreased and part price is lower verses single cavity tooling. The disadvantages are lower part quality due to imbalance in plastic flow and often the inability to run one part out of group without having to purchase the whole family of parts.
The metals used in molds can also greatly effect cost. Many of our prototype and small quantity tools are made from tooling grade aluminums.
Aluminum can be machined quickly and can be surface hardened or plated with a variety of materials. The main disadvantage is that it wears easily and, in cases of filled materials, it may wear out amazingly fast. It can also be easily damaged. Surface finishes can help the wear as can steel inserts in high wear areas, such as gates or meshing surfaces. Careful mold design can also overcome the disadvantages of aluminum. Aluminum is also often easily repaired in case of damage or wear. Aluminum is usually used in short run applications, but many production tools are now being made from aluminum, and aluminum tools can easily last hundreds of thousands of cycles.
Tool Steels for molds vary greatly. Prehardened materials such as P-20 can be machined fairly easily and polish reasonably well. P-20 can also be hardened from Rc 30-35 to Rc 45-50. It is a good choice in both short run and production molds. A similar material, NAK-55, cuts more readily and can be used in place of P-20 in many cases.
H-13 or S-7 can be used also but should be hardened before use.
A-2 and D-2 type steels make excellent cavity and core inserts when hardened (up to Rc 54 and beyond). They are most often employed in automatic tooling.
Whether or not you require a hardened tool depends on the number of parts you expect to run and the materials you are running. High volume tools should always be hardened as should medium volume tools that run with a glass or mineral or other abrasive material. When purchasing a hardened tool make sure the runner systems are also hardened.
Stainless Steel and other corrosion resistant steels are commonly used when using corrosive materials or additives are present in the plastic.
Beryllium Copper and other copper allows (AMPCO, etc.) are used for heat transfer as well as wear applications. There are also many other specialty metals, oil impregnated, surface treated, that have their place in mold making.
At APP we typically use aluminum or P-20 (or NAK-55) for low quantity tools. If wear is a problem we use hardened inserts of A-2 or D-2. Coppers are also commonly used when appropriate.
The greatest advantage of P-20 and NAK-55 steels is that they do not have to be hardened. Any time hardening is required more operations are required (grinding, polishing) and the risk of steel warpage is always present.
The Mold Quotation:
The quotation you receive should describe in detail how your mold will be built, the materials used in the tool and even an estimate of its production capacity.
When you receive several quotations you may find a wide discrepancy in pricing. Variations in mold prices are indicative of inadequate specifications or a misunderstanding of the specifications. Clearly specify what kind of tool you want built and demand a detailed description of the tool you are quoted. You cannot compare the price of an aluminum tool against that of one made of hardened tool steel.
Be wary of quotes that do not include a separate tooling charge or that describe the tooling as a non-returnable charge (NRE, NRSU, etc.). This means that you do not own the tooling--the molder does. If you receive a single lot quote for parts and tooling from American Precision Products that implies that the tooling will be useless at the end of the parts run specified. This is usually only the case in prototype situations.
You should also be wary of amortizing your tooling over a part run. The tooling does not transfer into your possession until all of the tooling charges are paid. If there is a dispute with your molder you may find yourself paying for the balance of a mold you do not own. This is not to say that amortizing your tool is a bad idea, just be aware of the drawbacks and put everything in writing! (see, tool ownership below)
Many, many, many people have be burned and embarrassed by this one. They go to move their tool to another molder because the price keeps going up each order for parts or for some other reason and they find out they do not own their mold! You must be very careful when purchasing tooling.
Make sure that tooling orders:
- list tools as a separate line items on your purchase order,
- describe tools correctly on purchase order--not as an engineering cost or setup cost,
- if you have arranged to amortize tooling cost over the parts make sure the agreement is spelled out clearly so that everyone knows when the tooling cost is complete and will be dropped. Insure that the tooling is listed separately and ownership of the tool is spelled out.
- If you have a legal department get them to go over any tooling order or consult some legal council.
If you do not own your tool you cannot remove it from the molder, argue over pricing (unless you buy a new one from someone else), and more importantly, the molder can use "your" tool for other customers or himself!
Note about amortizing:
We strongly discourage companies from amortizing tooling because of the confusion it causes (see comments aboveM). Realize that no matter what your PO says, you do not own the tool until it is paid for. We have seen instances where if amortized tools are not paid off in the agreed upon time then purchaser looses all rights to the tool. Amortizing a tool is not a simple exercise and it can be very easy to make a mistake in the agreement. Unless you trust your molder highly we suggest you seek your financing elsewhere.
Classifications of Injection Molds Up to 400 Tons
The following classification system is used by the Society of the Plastic Industry. It has been duplicated from Customs and Practices of the Moldmaking Industry, pages 11 & 12.
- 101 Mold
- 1 Million+
- Built for extremely high production. This is the highest priced mold and is made with only the highest quality materials. (Ed., Full mold drawings are typical, with fully interchangeable parts.)
- 102 Mold
- < 1 Million
- Medium to high production mold, good for abrasive materials and/or parts requiring close tolerances. This is a high quality, fairly high priced mold.
- 103 Mold
- < 500,000
- Medium production mold. This is a very popular mold for low to medium production needs. Most common price range.
- 104 Mold
- < 100,000
- Low production mold. Used only for limited production preferable with non-abrasive materials. Low to moderate price range.
- 105 Mold
- < 500
- Prototype only. This mold will be constructed in the least expensive manner possible to produce a very limited quantity of prototype parts.
- I Unit Insert
- Top quality materials for medium to high production requirements
- II Unit Insert
- < 100,000
- Similar to class 104 mold. Most commonly used insert. Low to medium production
- III Unit Insert
- < 500
- Similar to Class 105 Mold. Least expensive insert for very limited quantities. Insert build with the least expensive materials.
Bear in mind that this system is not exhaustive and there are many variations on this classification system (i.e., many high production molds are now made from aluminum). Also know that there are insert mold equivalents to every mold class and much gray area exists between classes. This classification systems is in the midst of review to address these very issues. Stay tuned for updates.
Important Note on Mold Classes:
Many mold makers will quote a class "A" or class "1" tool, etc. Please keep in mind that these designators have no established definition (especially class "A", "B", "C"). Your mold maker most likely is not trying to cheat you, these terms have been in use a long time, but to be safe insist that all paper work reflect the industry accepted callouts "101", "201", etc.