Optimizing your heat treat relationship.
Historically, heat treating services have been viewed by foundrymen as a necessary evil, needed to correct mistake castings or because of customer specifications. However, within the last 20 years, the amount of salvage or corrective heat treating performed has decreased dramatically to less than 5% of the overall casting workload. This is due, in large part, to better foundry control, more technologically advanced equipment in melting and molding, and an adherence by foundries, throughout their production process, to stricter casting procedures.
In response, heat treating services have evolved to help metalcasters streamline production and meet the tightening end-user specifications. In actuality, heat treatment facilities have become an extension of the foundry cleaning room and the metalcasting process. They have shifted emphasis from providing only after-cast services to establishing themselves as an integral part of the casting production process. In addition to providing value-added services like warehousing and drop-shipping of castings, heat treating services can aid foundries in improving their casting production speed while simplifying the entire process. Although the fundamental goal of heat treating services has remained the same - to improve casting properties - the value-added services they perform have changed their relationship with foundrymen.
This article will examine the evolution of heat treating services and what it can provide to the metalcasting process. It also will describe what a foundry should consider when choosing a heat treating service and how to optimize this relationship once it has been established.
Role of Heat Treat Services
In basic terms, heat treatment is the application of heat (via a furnace) to a casting followed by controlled cooling (via a gas or liquid medium) to modify one or more of these casting attributes: hardness, microstructure, mechanical properties or residual stress formed during solidification. However, the basic definition for this scientific process doesn't define the role of the heat treat facility.
Heat treat facilities can provide five benefits to foundries: increase foundry output, reduce alloy cost, fix casting mistakes, reduce machine tooling costs and provide value-added services.
The ability of a heat treat facility to increase foundry output is related to its ability to simplify production. Most foundries have castings that are different, in terms of properties, in their production runs. These different castings often cause the molding line to slow down or to be interrupted to accommodate these different castings. Whether it is due to specifications that require better hardness or less elongation, the casting may need special attention and doesn't run well with the rest of the product mix. In the foundry's effort to make the part within customer specification as-cast, the molding line is slowed down to ensure proper casting, reducing overall productivity.
At this point, the heat treat facility should become an option. If the problem is the casting's large cross-section size (which forces a slower shakeout to achieve hardness throughout a larger casting), the foundry can run the molding line at its rated molds per hr, shake the castings out hot and depend on a heat treating service to put the castings in hardness specification. Depending on the quantities involved, this could save a foundry all or part of a production shift, in comparison to pennies-on-the-dollar heat treat cost.
As an example, a ductile iron foundry was running a 75-lb casting on its vertically parted molding line. The foundry needed to achieve a 60 tensile-45 yield-12 elongation part, so it was running the line, which had a peak efficiency of 300 molds/hr, at only 80-100 molds/hr - 33% capacity. Looking for a solution in heat treat, the foundry ramped the line back to normal production, shook the parts out hot and had the heat treating service anneal the castings into the desired hardness. The heat treating service is able to simplify production by taking on some of the casting property responsibility.
A second benefit of heat treating is reducing alloy cost by allowing foundries to eliminate some of the alloys they pour. Many foundries must pour a variety of metal grades to achieve the various necessary casting properties. However, if a heat treat facility is used, these foundries could pour a base metal and let the heat treating service air quench or liquid quench the castings up to the higher property requirements of the other alloys, thus reducing the alloys the foundry needs to melt. In the case of iron, a normalize or air quench can increase the properties of a casting from 65 tensile-45 yield-12 elongation to 80-55-06, and a liquid quench can increase the properties from 65-45-12 to 100-70-03.
The third benefit is the most recognizable - a heat treating service's salvage work. If a casting is too soft after shakeout, heat treating services can quench the hardness back up. If the casting is shaken out too hot and too hard, the facility can anneal and soften the casting. Lastly, if a casting is poured with iron carbides in it, a carbide removal and full anneal will remove the problem. Although the process is generally more expensive than standard heat treat, salvage heat treat is a better option than sending a lot of castings to remelt.
The fourth benefit is improving the casting's machinability. Heat-treated castings are more easily machined than in-specification, as-cast parts. In a 1992 test performed by a heat treating service, a machine shop was asked to compare the machinability of two groups of ductile iron castings under 40 lb - one was cast to 80-55-06 and one was heat treated to the same. The heat-treated castings showed 38% longer machining tool life and 15% increased productivity. These advantages offset the cost of heat treat and provided a significant per-casting savings.
The fifth benefit of heat treat facilities - value-added services - includes drop-shipping and warehouse services. Drop-shipping allows a foundry to ship its castings to the heat treating services for processing and then have the treated castings shipped to the end-users from there. This eliminates freight costs and valuable time that would otherwise be wasted shipping the castings back to the foundry. The heat treating services then become the final inspection point for the castings before shipping. Thus, the competency of the heat treating services and the strength of communication between your two operations are critical in such a relationship.
Accompanying the drop-ship is the possibility of warehouse services. Customers of castings may only require a limited number of castings per order that are delivered at short time intervals. However, high-production foundries do not produce small orders of castings at short intervals, and heat treating services do not process small amounts of castings at short week intervals. The costs involved with slowing production to meet customers' demands are not effective for either operation. So that foundries can avoid cluttering their shops with castings awaiting shipment, some heat treating services will provide a warehouse service, in which they will heat treat the full production run of castings and provide storage as the end-user's demand dictates shipment.
Securing Heat Treat Services
The evolution of heat treating services as an extension of the foundry cleaning room has made the choice of facilities an important step for foundries. Not all heat treating services can provide the benefits detailed above, therefore selection should be based on the needs of the foundry and its castings.
Answering these several questions about a prospective heat treatment facility should shed light on the possibilities:
* Quality - Does it have a quality system? Is it quality-certified by any outside sources (ISO/QS-9000) or by its customers? Has it received any quality awards?
* Delivery - Does it have an in-plant turn-around time that meets your production needs? Does it have a history of on-time deliveries? Will it drop-ship to your customer for you? Does it operate its own trucks for pickup and delivery?
* Capacity - Does it have the right size equipment for the work your foundry wants to send? Does it have the throughput capacity to handle the volume you want to send? Is it willing and able to add capacity or processes to meet your needs?
* Fiscal Soundness - Does it depend on today's production to pay last month's bills? (Secure a Dunn & Bradstreet report to make sure.) Does the heat treating service have a proven track record of investing profits back into its facilities?
* Service - Is it willing to work with your foundry on developing new work and soling problems? Is it willing to interface with your foundry's customers? Does your foundry receive timely, accurate responses to questions and requests for quotation? Will it warehouse finished material and provide just in time delivery?
* Technology - Is the equipment modern and well maintained? Is there a trained metallurgical staff? Is the laboratory capable of providing the testing your foundry requires? Does it subcontract outside sources for testing it cannot perform?
* Net Value - Is it competitive for the services it provides? Are you receiving sufficient value for your heat-treat dollar?
The level of technology within heat treating services varies just as it does with foundries. At the most advanced end, a heat treat facility may contain electronically-controlled furnaces that allow for zone adjustment of atmosphere and temperature, time controls of how often trays of castings should be introduced to the furnace, and drop loaders to automatically load castings onto the furnace belt. These operations remove a majority of the human element from the process.
At the other end, there are smaller operations that are run on manual labor, without the advances of technology. These operations can accommodate a foundry with smaller loads of castings more easily, in addition to offering more flexibility to a customer. For foundry management to determine the best heat treat situation for itself, it will need to address the answers from the questions and determine what specifics it requires from an operation for its castings.
Lines of Communication
With the heat treat facility acting as an extension of your foundry, the line of communication between your two operations should be as clear as the departments within your plant. For this to occur, the two entities must develop a common language to focus on the task at hand - shipping the best possible castings to customers. The effort used in establishing this vital communication link will repay itself through the previously detailed capabilities.
To maintain clear lines of communication, the foundry must work with the heat treating service to:
* clearly define quality standards with a production part approval plan (PPAP) and advance production quality planning (APQP);
* agree upon an acceptable turnaround time;
* give the heat treating service advance shipping notice so it can pre-schedule castings, as surprise loads will not receive the same attention;
* define the problems with salvage work like chemistry, inoculation and shakeout. If they aren't identified and the material has to be reprocessed, the foundry will be expected to pay for it;
* provide"actual" (by cast date), not "typical," chemistries with each load of castings, because heat treat is a science, not an art;
* agree upon a test location for hardness and microstructure before sending the work out;
* agree upon a sample quota for testing and the type of post-heat treat certifications that will be required.
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If your foundry needs to specify a heat treatment cycle for a shipment of castings, then the heat treating service will charge higher-than-normal prices since a specified cycle can disrupt its optimum productivity.
In terms of pricing, do not expect the heat treating service to quote your shipments blindly. The old days of "How much per lb to anneal?" have vanished with the advancement of QS-9000. Heat treating services will ask for prints, specifications, APQP and a trial run to quote on an individual part number basis.
Heat treating is an engineered service, not a commodity, thus the heat treating service should be involved at the beginning of the casting quoting process. When a foundry is securing a job, it should consult its heat treating service to determine what it can offer. When heat treat is contracted as an afterthought after the job has been secured, it can sometimes have a negative (profit-reducing) impact on the original quoted price.
Lastly, it is important for the foundry to learn the heat treat terminology (see Heat Treat Terminology sidebar). For example, the term "anneal" is generic and means "to soften," but there are several types of annealing that receive their names from the microstructure desired or the temperature at which the parts are processed.
The secret to establishing an optimum relationship with a heat treating service is communication. If a foundry communicates with the heat treating service to tell them what type of casting it is working with and what the end product should be, then the heat treating source can use its expertise to produce results for the foundry and its customers.
RELATED ARTICLE: Benefiting from Out-of-House Heat Treatment
Any foundry, large or small, decides for itself whether or not to do heat treating under its own roof or contract it out to a commercial heat treat shop. However, the notion that heat treat operations can be viewed as a fixed cost in a foundry's production cycle has vanished. For a foundry to be competitive in today's world market, heat treat must be an integral part of the casting process and a direct, variable cost.
This belief has pushed heat treatment operations out-of-house, relying on the outside companies' expertise to provide benefits. The advantages outside heat treating sources offer are:
* lower cost. As an energy intensive business, the heat treat shop enjoys the lowest rates for gas or electricity. A foundry may pay 2-3 times as much. Moreover, a commercial shop uses its furnaces 24 hr a day, seven days a week, while a foundry seldom uses its equipment continuously, suffering waste in warm-ups.
* higher quality. Because heat treatment is the core competency of a commercial operation, the company and the people it employs must be of the highest caliber and stay current with new technologies and regulations. A lack of skilled help, spoiled work and defects are not tolerated.
* the ability to conform to specially designated environmental laws. OSHA's hazardous communication standard, EPA's regulations regarding used oil, RCRA small quantity generators, underground storage tanks and water treatment, and the Clean Air Act pose their own paperwork trail for fear of noncompliance that any heat treat operation, inside or outside, must know.
Heat treating is no longer just a burden and a fixed cost. It is a component of the manufacturing process that may not fit into the macrostructure of the foundry's philosophy of making the best casting for the marketplace.
- M. Lance Miller, Metal Treating Institute, Jacksonville Beach, Florida
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|Date:||May 1, 1998|
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