Workholding

Quick Change Fixturing: The Link to Manufacturing Efficiency

I. Efficiency of a Well Designed Quick-Change Workholding System

A well designed workholding system holds the part in a fixed position to allow for precise fabricating within a specified tolerance.  Workholding is comprised of two primary components:

  • The actual workholding tool, such as a vise to hold the piece in place.
  • A device to firmly attach the workholding tool to the machine. This can include the use of fixture plates, universal T-Slot bolts, clamps and other devices which can firmly position and hold the part into place.

Today there are more quick change technologies available than ever before for multi-axis, horizontal and vertical machining centers.

Highly engineered quick-change workholding systems allow for significantly more machining time out of every shift.  There are systems that offer dramatic improvements and savings under the spindle when compared to traditional workholding methods.

Manual Systems

Some manual mounting systems can shave up to 75% from your set up times by implementing a quick change fixturing system for a fraction of the cost of traditional methods, such as; clamps, T-Slot bolts, strap clamps, locating pins and more.  A manual quick change system can also be enhanced with either pneumatic or hydraulic release for faster part change over.

Some provide repeatability of up to +/-0.0005" (+/-0.013mm) or better, all allowing for increased uptime and much higher accuracy.

By using Ball Locking shanks with receivers, Quick Locating System fixture plates and subplates, the operator can quickly and accurately locate and hold down fixtures to the machine table in minutes.  These specialty ball locking shanks incorporate internal ball bearings.  As the hex key is tightened the shank locking mechanism moves the spring-loaded ball assemblies outward, locking them into place.  They can have holding forces ranging from 625 lbs. for a 1/2″ (13mm) shank to 15,200 lbs. for a 2″ (50mm) shank.

To mount the system receiver bushings are preinstalled into the subplate or fixture plate, and then a vise can be easily mounted without the need for indicating.  Simply install the shanks into the jigsaw base of the vise and tighten them down with a hex key.  Then load the parts into the machine and it’s ready to go.

This method is far more efficient than setting up with a traditional vise, which is time consuming and labor intensive.  Using the right quick change system can allow your spindle to be cutting, not waiting to cut.  In addition, some of these set-ups can hold two parts at once, eliminating the need for an extra set-up, while doubling the production.

See Quick Change system in action

Automated Systems

There is revolutionary technology available that allows for fixing, positioning and clamping in a single operation.  The most efficient is a Zero Point Clamping System which allows the operator to fix, position and clamp in a single step.  Zero Point Systems can cut set up times by up to 90%.  They are available with either pneumatic or hydraulic release.  The positive locking locating modules allow operators to quickly change out large and small fixtures with extreme accuracy and minimal effort.

Extremely accurate automated mounting systems permit accuracy, speed and repeatability of up to <0.0002” (0.005mm).

The features of Zero Point Systems include pull studs that can be installed directly into the workpiece, which is ideal for large or heavy parts.  They can have corrosion-resistant construction suited for use in food service, pharmaceutical and chemical applications.  Plus, their variable dimensions allow for optimal use of traverse displacement.

Zero Point Systems can be ideal for a variety of mountings.  Their features include Installation Mounts which are manufactured to match specific machine table requirements, Surface Mounts that are designed for table surface installation and Flange Mounts that have internal or external line options, making it easy to adapt to existing columns or plates with low installation depth.

To recap, many automated system benefits include:

  • High Accuracy – .0002” Repeatability
  • Speed – Air or Hydraulic Release
  • Automation – Release can be controlled by the program
  • Flexible Positioning of Receiver Module for Large and Odd Shape
  • Easy Locating Self Centering Stud
  • Application Opportunities Beyond Machining

 

II. The Benefits of Quick Change Fixturing

A fully optimized workholding operation provides versatility in machine automation and robotics applications.  It will:

  • Reduce the number of set-ups required
  • Maximize machine capabilities
  • Allow for complete utilization of the machine table envelope
  • Reduce changeover time
  • Minimize spindle down-time
  • Free-up additional capacity
  • Increase overall output, productivity and profitability

 

Any of these systems can be custom made to the specific needs of the application.  When selecting a manufacturer of a custom workholding system it is important to consider those companies with broad product design and build capabilities.

III.       Conclusion:  Cost Savings Associated With Quick Change Fixturing

The cost savings associated with quick change fixturing can be substantial.  It is not unusual to eliminate two hours of set-up time per shift, which in an average shop can provide approximately $50k in annual overhead cost savings at typical shop burden rates.  Perhaps more importantly, the two hour savings can provide an additional 500 machine hours/shift per year in available machine time.

In the case of one company, the average set-up time was virtually eliminated over their prior process, by:

  • Reducing average set-up from 3 hours to a few minutes
  • Saving approximately $68,000 in overhead cost
  • Gaining an additional 750 machine hours

Quick change fixturing can play a significant role with highly increased efficiencies in manufacturing production.  It is all about saving time and money by changing what is under the spindle, not on it.  When selecting the right workholding partner with the broadest line, operators of CNC and other automated machining can realize efficiencies, cost reductions and increased machine time that will set them ahead of the competition.  Securing jobs for more prototyping is a great opportunity for growth in machine shops.  Yet, for major manufacturers the benefits of quick change fixturing can provide tremendous opportunities to gain market share.

Case Studies

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Workholding

The Significance of Workholding

How Workholding Increases Output

Horizontal Machining Center with Jergens Vise Column using Ball Lock Mounting system
Horizontal Machining Center with Jergens Vise Column using Ball Lock Mounting system

When machining a part, workholding is a term used to describe holding the part in a fixed position to allow for precise fabricating within a specified tolerance. Workholding is comprised of two primary components:

1) The actual workholding tool, such as a vise to hold the piece in place.
2) Positioning and firmly attaching the workholding tool to the machine. This can include the use of fixture plates, universal T-Slots, 4 or 5 axis components and many other devices which can firmly position the part.

The second method of workholding includes the creation of a manufacturing cell where the placement of the part is secured to quick-change pallets in order to easily switch workpieces during the machining process. This allows the operator to automatically or manually switch the workpiece position or replace it for performing a subsequent operation, all without interrupting the work in process (i.e. machining parts on other pallets).

The pallets holding the workpiece allow for high repeatability. The self-seating of these pallets allows them to be placed into the exact same location each time. This significantly reduces setup times, from what otherwise would take hours, down to just a few minutes. The addition of a trunnion table can serve as a fourth axis to allow for additional machining without additional set-up, and if necessary it can provide the opportunity to add more components to be machined by simply loading additional pallets concurrently.

Having a workholding system increases productivity and throughput which generates more production uptime and greatly reduced set up and changeover times. In addition, it allows the operator to make changes to the job quickly, ultimately increasing production output. And changing workpieces in a highly repeatable manner significantly increases the quality of the finished part. All of this is accomplished without interrupting production. Often, too much time is spent mounting a single workpiece in a machine. The primary function in streamlining production is to develop a workholding solution that optimizes the machining of multiple parts at once while maintaining tight tolerances.

Workholding Benefits

• High repeatability
• Increased spindle uptime
• Quick-change setups; from hours to minutes
• An increase in the number of parts per shift
• Measurable increase in accuracy and quality

Selecting the Right Workholding Solution
Whether for a small prototype shop or a large production facility, the selection of the best workholding solution is critical to any operation. A system that is proven to increase productivity and throughput by decreasing set up times and changeovers will result in more machine uptime, as long as the components are as rugged and versatile as the OEM machine itself.
Often, the versatility is more a function of a workholding solution, then the machining equipment. The objective is to have a solution that provides a significant, measurable and fast return on investment (ROI): To affect the ROI, the workholding solution must:

• Dramatically increase productivity and throughput
• Speed set ups and changeovers
• Show an increase in machine uptime

Though there are many standard workholding components available, many applications call for customized solutions that provide extreme accuracy and high repeatability. A common challenge in many of these applications is accommodating vertical milling along with multiple-axis machining. For instance, applications that benefit from five-axis machining where the cutting tool can access the workpiece from multiple sides and angles must have adequate space to accommodate all components.

Some of these customized solutions are not only extremely versatile, but are also comparatively affordable and easily programmed. It is important to select a company that specializes in the development of workholding solutions for complex geometry and can develop a cell which fixtures the parts on quick-change pallets so the workpiece can be placed at the same location of the cell at every operation. Some workholding companies design 5-axis machining that achieves up to 0.0002” repeatability and unrestricted access to the part, allowing for part-to-part changeover in less than one minute.

The Benefits of 5-Axis vs. 3-Axis Machining

When all or most sides of a part require machining, it is most efficient to utilize multi-axis workholding. However the jaws, other vise components and the machine table itself can restrict access to all sides of the part. In traditional multi-axis cutting the machine must be stopped and the part needs to be repositioned to machine the next surface. Even 3 simultaneous machining axis on a rotary table can limit, or at the very least, slow the machining process. However a well-designed, highly repeatable, 5-axis machining center allows for fast and repeatable manufacturing of even the most complex parts.

Modern multi-axis machining can be described as:

• 3 Axis: Vertical milling machine with CNC computer controls moves three axis: X right to left, Y front to back and Z up and down, controlling movement for the cutting tool
• 3 + 2 Axis: Three plus two machining uses a vertical machining center with a tilting rotary table producing complex parts like a full 5 axis machine tool, but the last two axis are for positional not simultaneous movement
• 5 Axis: A full 5 axis machine tool is able to move all axis’s simultaneously allowing fewer setups and faster machining times

The benefits of 5 Axis Machining Include:

• Reduced number of fixtures & set ups
• Reduced number of operations with 5 sides being machined simultaneously
• Part remains in single clamped position, reducing the potential for error
• Simplifies the machining of complex shapes
• Reduces the total programming required
• Improved part quality due to increased repeatability

The advantages of combining multi-axis and 5-axis machining capability:

• Placing the part into the optimal machining position
• Standard modular components
• A rapid quick change system
• Configure the machining center based on specific need
• Non machine specific (except subplates)
• Easily transfer components to different machines
• Reset for machining of other parts

Conclusion: The Cost Savings of Workholding – Maximizing ROI

Some companies provide clearly defined on-line calculators to show the return on investment for a customer’s workholding solution. Using these calculators graphically represents the savings to the shop or multi-station factory, right down to savings that can be passed along to the end customer. Dollars saved are reflected in:

• Reduced Set-Up Time
• Reduced Tool Change Time
• Calculates Recovered Machine Time
• Calculates ROI on Cost of Tooling Required

To receive more information on Workholding Solutions for manufacturing applications, click below

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Sources:
CNC Cookbook
Production Machining 1
Production Machining 2
Modern Machine Shop
SME

For more information on best in practice workholding solutions, visit Jergens Workholding.