Lean Heat Treating System incorporating modularity of design, flexibility of equipment and process and adaptability to product change. The system was originally designed to process Nitralloy slugs up to approximately 4" (100 mm) prior to nitriding. Hardness variation (surface to core) was held within 2 HRC. As aerospace and automotive product needs change, the system can be switched to perform processes such as low-pressure vacuum carburizing of both conventional and advanced materials, high temperature sintering and hardening of powder metallurgy and tool steels, and brazing of stainless steels.

Why Lean?

The last ten years has seen the long-standing practice by furnace manufacturers of supplying "stand-alone" pieces of equipment change to that of building systems completely integrated into the manufacturing flow. Recognizing the reality of global competition, there is new emphasis being placed on improving the overall efficiency of manufacturing by using lean manufacturing strategies (Fig. 1).

Fig.1. Lean Manufacturing Strategy
The steps involved in a lean manufacturing strategy encompass an extended 5S strategy - to that of 5S+1. These steps are:

  • Sift - decide what things you need to accomplish your work, and remove from the workplace all items that are not needed for current production (or clerical) operations.
  • Sweep - decide which things you do not need to do your job, and remove them from your workplace.
  • Sort - ensure that people can do other people's work when they are not at their own workstation
  • Standardize - create a standard for everything, and try to use the same methodology and style throughout the manufacturing operation.
  • Sustain - make the 5S + 1 methodology a living concept performed on an on-going basis.

    and, in addition, guarantee

  • Safety - in everything that's done, safe practices and anticipation of controls to assure worker safety is mandatory.

    Fig. 2. Lean Heat Treating Strategy
    Heat treating, a core competency as part of the success of any manufacturing strategy, means equipment manufacturers must adapt to this "on demand" philosophy. The 5S + 1 strategy for lean heat treating (Fig. 2) involves:

  • Strategize - optimize part and workload configurations to minimize distortion, reduce or eliminate post heat treatment manufacturing steps and achieve the best possible quality
  • Synergize - organize and coordinate processes to reduce cycle times and increase throughput
  • Service -perform the necessary actions to assure uninterrupted operation and maintain production throughput
  • Satisfy - maintain absolute quality assurance
  • Support - anticipate equipment and/or process problems to avoid unscheduled downtime

    and, in addition, be sure to be able to

  • Synchronize - create a safe and mistake-proof working environment both within the heat treatment operation and extending to the entire manufacturing operation.

    Fig. 3 Modular continuous vacuum furnace for hardening high speed steel saw blades for the power tool industry.

    Why Conventional Heat Treat Technology Fails

    One runs the risk in the manufacture of heat-treating equipment to ignore the needs of lean manufacturing and lean heat treatment by failing to design equipment with adequate flexibility to meet the demands of modern manufacturing operations. This ability to anticipate future need given the changing face of manufacturing is what separates an adequate supplier from a good one. Furnace and equipment design engineers must understand that changes in materials, manufacturing methods, processes, and even physical plant locations is a part of the new reality and an absolute part of their design strategy. The era of relying on what has been built in the past is over. Whether the heat treat system is large or small, simple or complex, the ability to rapidly alter the design to handle whatever may be required must be built into the system as supplied.

    Fig. 4. Batch vacuum furnace for hardening roll threading dies reconfigured into a continuous flow design.
    Today, corporate edicts are demanding lean manufacturing and lean heat treatment strategies; they require all manufacturing equipment to be environmentally responsible, conserve energy as well as other natural resources, produce small lot sizes quickly, and be mobile both within an existing facility and have the ability to move from site to site. Equipment must be engineered for use anywhere in the world. In addition, most companies are insisting that a furnace manufacturer support their equipment on a continuous basis no matter where it is located in the world. These demands are not unreasonable, and innovative companies have evolved strategies to support these needs.

    Fig. 5. Multi-directional continuous vacuum furnace for hardening of high speed steel tools having multiple quench (oil and high pressure gas) and multiple process (annealing, hardening, low pressure carburizing and carbonitriding) capability.

    Lean Heat Treat Equipment Requirements

    Lean manufacturing demands we apply multi-tasking skills to our heat-treating operations. We must have full control of all heat treatment equipment and process variables. The keys to achieving this involve designs with inherent:

  • Modularity. Having a solid platform from which expansion can take place is essential. Expansion at low cost, high value added, and the ability to changeover at critical velocity is mandatory.
  • Continuous vacuum furnaces (Fig. 3) are able to meet high production demands, add additional processing chambers as production increases, provide mobility by being able to be moved throughout the plant (or from one plant to another) and by being built in a "quick disconnect" fashion for ease of expansion and maintenance.
  • Adaptability. The ability to change cycles or processes quickly, from load to load or lot to lot.
  • Batch style vacuum furnace (Fig. 4) converted into a continuous vacuum design by simply removing a rear door module and adding a loading module. These units can run both high temperature processes such as sintering and lower temperature processes such as ferritic nitrocarburizing all within the same platform.

    Fig. 6. Combination design capable of atmosphere and vacuum processing of powder metal residential and commercial building control components.
  • Flexibility. Having capability to process a variety of parts within the same heat treatment center is a lean manufacturing necessity.
  • Multi-directional flow designs (Fig. 5) take advantage of the ability to move through the system in either direction and perform different heat treatment processes either independently or simultaneously.
  • Compatibility. The ability to combine different technologies such as atmosphere and vacuum in a common platform allows added versatility.
  • Combination atmosphere and vacuum system (Fig. 6) to meet the process demands for both low temperature and high temperature operations for dissimilar processes without sacrificing the ability to produce product in a continuous flow automated system.

    Fig. 7. Continuous mesh belt hardening furnace for processing scissors blades.

    Integration into the Manufacturing Flow

    The ability to utilize a small footprint allows integration into cellular manufacturing so that product does not necessarily have to be moved from where it is being produced to a remote heat treatment operation. Both atmosphere and vacuum systems have been designed and successfully employed for in-line (Fig. 7), on-line (Fig. 8), and centralized ‘heart' cell (Fig. 9) manufacturing operations.

    Fig. 8 Batch vacuum furnace for combination vacuum brazing and vacuum carbonitriding of hand tools.
    In-line systems service the needs of a single product as it is being produced in a dedicated manufacturing operation. On-line systems service a family of products having common heat treating requirements and receive parts from a number of operations simultaneously. Heart cell operations service the needs of an entire facility and often are the most demanding in terms of automation and flexibility. Many times multiple types of heat treating and ancillary equipment must be integrated into a single high throughput operation.

    Fig. 9. Continuous vacuum furnace system designed for high volume vacuum sintering and hardening of powder metal gears for the automotive industry.

    Lean Applications

    Low pressure vacuum carburizing, a patented[1] Hayes invention (Fig. 10), is a process with advantages that are now well recognized throughout the industry. Hayes has perfected and continues to advance the technology with their research into various carburizing gases, gas distribution methods and innovative designs such as continuous systems, which can be directly loaded while at operating temperature (Fig. 11).

    Fig. 10. First ever vacuum carburizing patent

    Rules for Lean Manufacturing in Heat Treatment

    There are eight simple rules for success in heat treatment. They are:

    1. To know, metallurgically, what it is you want to accomplish
    2. To be able to predict the outcome of the heat treating operation
    3. To have repeatability built into the process
    4. To use state-of-the-art heat treating equipment and methods
    5. To be able to adapt to changes in manufacturing operations
    6. To understand and not compromise on quality control measures
    7. To control costs
    8. To use automation and equipment in a lean manufacturing environment

    Fig. 11. Self-cleaning vacuum carburizing furnace capable of being opened at temperature

    From Raw Material to Finished Product

    Modular engineering together with real time control methodology applied to both equipment and process variables allows us to integrate heat-treating systems directly into today's lean manufacturing strategies. Antiquated heat treating departments are being broken up and parts produced where they are being manufactured. Coupling similar operations together increases efficiency and continuous work flow. The future of heat treating as a competitive technology will be assured by equipment manufacturers willing to accept that lean manufacturing strategies apply to the heat treating operation as well as all other areas of manufacturing. IH

    Additional related material may be found by searching for these (and other) key words/terms via BNP Media LINX at www.industrialheating.com: Heat treating, lean manufacturing, lean heat treatment, continuous vacuum, modular engineering