February 2007 Edition

SOFTWARE SOLUTIONS

Get the Most from CNC Automation Investments

Eight steps that take full advantage of automation capabilities in most shops

by Mike Rogers, Director of Automation, Hirschmann Engineering USA, Inc.

To remain competitive in a global economy, U.S. companies are faced with producing parts faster, with tighter tolerances, and lower costs. These competitive pressures also face job shops and contract manufacturers. Market demands are forcing large and small companies to determine whether production capabilities are operating at maximum efficiency and if companies are getting the most out of their capital equipment investment.

Besides global competition, U.S. shops face the tightest job market in more than 30 years. Skilled machinists are rare and good ones are hard to keep. When qualified personnel are not readily available, companies must to turn to trade schools or apprentice programs. The cost to train and keep good quality employees is steadily increasing due to the short supply of skilled workers and the growing demands for technical- and computer oriented skills.

One way to combat these problems is to increase the use of CNC machine tools. While CNC machine tools are abundant in most shops, many companies have not extracted the full potential from the equipment. This is because the ideas that are inherent in CNC machining have not been expanded to include the entire shop. Most companies only use 1,000 to 3,000 hours per year per machine out of a potential of more than 6,000 hours each year of actual billable time per machine. CNC machines quickly process work without operator intervention, but once the job is finished, the parts may sit, waiting for a bottleneck further down the manufacturing line to clear.

Benefits of Automation
There are 8,760 hours in a year. Typically shops get 1,000 to 2,500 hours of attended machining time per year with operators working one shift five days per week. If machines are not running during the remaining unattended time – up to 6,000 hours per year – they are standing idle more than 70 percent of the time.

How can shop owners get to that magical 6,000+ machining hours per year? By applying a systematic automation approach to the shop and CNC machine tools. Even small shops can reach the high productivity rates once thought only possible with high-volume production work.

A secondary benefit of applying these principles to a job shop is that the shop will become more organized by virtue of the structure required to implement an automated system. Work can be setup and processed without constant human supervision. Changes in the work schedule can be made quickly and easily since provisions for flexibility are at the heart of the automation concept.

The ultimate goal is an increase in shop work capacity without large investments in workforce. Remember, CNC automation is not something that shops can purchase; it is a process that people can apply to a shop.

The Eight Steps to Successful Automation Implementation
A successful automation program implementation process in a CNC job shop can be refined to eight steps. The steps move a shop closer to the ultimate goal of a lights-out machine shop. Every step will also help a shop become more organized and more profitable than before. The improvement in profitability helps finance the future steps required to reach increased machine use.

For success, each step must be taken in order and implemented into the shop’s day-to-day work habits. Like the weak link of a chain, a step not taken creates a bottleneck that drains productivity gains and profits created by other investments in the process. Even the small shop can afford to take these first steps since the steps require a relatively-small financial investment. The greater investment is believing in the concept and following it.

Step One: Work Standardization
Standardize the process not the workpiece. Adding an automated system to the shop does not mean that every part in the shop must fit a particular shape and size, or be a production job of 5,000 to 100,000 parts.

The first step toward automation, especially in a job shop, is to review the work and look for similarities. This does not mean limiting the shop’s business to one type of die or mold. Every shop has inherent standard specifications in place by the nature of the equipment and expertise available. Those should be found and codified.

Once a shop recognizes work similarities, a system for automating production of similar parts can take shape. If a shop does 80 percent of its work within one work envelope, and the remaining 20 percent varies, it does not make sense to automate 100 percent of the work. This would require tooling system and automation equipment that would be considered overkill up to 90 percent of the time.

The more cost-effective approach is to automate and improve the throughput of the greatest percentage of the work. More time is then available to manually attend larger work on stand-alone equipment outside of the cell.

Determining the work envelope for the cell lets shop management select the proper tooling system for the standard interface between the workpiece and machine tool.

Step Two: Job Planning
Job planning identifies and documents the steps required to move a workpiece from raw material to finished dimensions and deliver it to an internal or external end-user.

This sequence includes the design phase, CNC programming, raw material preparation, presetting, scheduling, machining, and finishing. Adhere to this sequence to process work in an orderly manner. Creating a job plan helps predict shop floor bottlenecks. Machine tool use is optimized when a proper plan is in place for each workpiece.

Step Three: CNC Programming
Most shops have more than one programming system for its CNC needs. To streamline CNC programming, a shop should commit to a standard programming environment.

Workstations involved with programming the cell should be set up with a competent, integrated CAD/CAM system that provides all of the programming capabilities needed in the foreseeable future. If there is more than one seat of CAD/CAM software being used to program parts for the cell, each system should have the same software release level, with similarly-configured hardware.

The CAD/CAM software must have clean post-processors, optimized for the machine tools involved in the cell. To simplify programming repetitive features, these optimizations should include program start, program end, special function assignments, and macros. A major waste of resources is a machine tool with special machining functions unsupported by CAM software.

Selecting a standard programming technique eliminates the need for programmer interaction with cell operators about every job detail. It is unacceptable to add the workload of shop-floor program editing after post-processing.

To create programs that machine operators can understand, each programmer must adhere to a documented set of standard programming conventions. These conventions should include standard entry and exit routines, standard cutting directions and cutter offsets, and other similar conventions.

Step Four: Raw Material Preparation
To obtain an automated system’s greatest efficiency, shops must establish standard production guidelines for raw material blanks. Considerations should be made at the design level for the mounting of the raw material blanks onto a selected tooling system. Shops should build and maintain an inventory of pre-machined workpiece blanks for standard mold or tool components. A cell should never be idle because raw material is not available.

Standardized raw material preparation could include items such as
·workpiece blank sizes;· established and programmed start hole size and location consistent with wire EDM thread position or mill start positions;
· workpiece reference surface machining to guarantee tool system part registration accuracy;
· standardized part pickup procedures so the same references are used across multiple processes;
·and workflow through the shop.

Workflow is related to Step Two: Job Planning. Shops must address these issues to streamline part workflow:
· Can workpieces move from machine to machine around the shop in an organized manner?
· Is it possible to locate a particular workpiece in production on the shop floor?
· Are the machines on the shop floor arranged in a logical manner that matches the production process or are they placed wherever they fit in the shop at the time they were purchased?

There are fudge factors due to standardization required by adding an automation cell to a shop. Shops should not tolerate them. Each part must be produced to exact tolerances for it to fit into the overall process. Shops should require part production consistency when implementing an automation system. Consistency goes hand-in-hand with the implementation of ISO quality standards undertaken by so many shops.

Step 5: Workflow Through the Shop
Workflow is somewhat related to the Job Planning. When examining efficient workflow, ask these questions
· Can the workpieces be moved from machine to machine around the shop in an organized manor?
· Is it possible to locate a particular workpiece that is currently in production on the shop floor?
· Are the machines on the shop floor arranged in a logical manor that matches the production process or are they placed wherever they fit in the shop at the time they were purchased?

These are the issues to be addressed to streamline the workflow of a part. Due to the standardization required by adding an automation cell to a shop,

These fudge factors can no longer be tolerated. Each part must be produced to exact tolerances for it to fi t into the overall process. Part production consistency required when implementing an automation system goes hand-in-hand with implementation of ISO quality standards.

Step 6: Palletization and Presetting
A modern tooling and palletization system is the key to automation principles in a shop environment where no two parts may be the same. The tooling and palletization system provides a standard interface to the machine tool while offering flexibility in workpiece mounting.

The latest versions of automationready systems enable workpiece mounting to fixtures or pallets outside of the machine tool and then bringing them into the machine – with high-accuracy repeatability – and locating them without wasting machining time for part pickup.

Improved accuracy, setup consistency, and increased availability of machining time offset tooling investment. The return-on-investment period for these systems can be as little as three months due to the gains in machining time.

Shops should pick a tooling system that best meet its needs. Multiple tooling systems are useful if the workpiece must be removed from the tooling system during production, i.e., one operation before heat treatment and another after.

In those cases, shops should make provisions for remounting and locating the workpiece onto the second system when the parts return.

There are two options for off-line workpiece presetting:

First, and most common, is the mechanical presetting station based on the tooling system chosen for the cell. This station permits parts to be clamped and aligned parallel to the machine axes, eliminating the need to level and align work in the machine.

The operator must locate the part in the machine tool with its measure functions, since this presetting station can not locate the workpiece in reference to the tooling. Standard reference locations for part pickup can be implemented that allow the use of automated pickup cycles in the machine.

Second, is the use of a Coordinate Measuring Machine – CMM – as a presetter. In this case, part alignment is set to match the machine axes; part measurement data can also be taken in reference to the tooling system. Once this done, the data can be passed directly to the system or machine tool control via a serial or network link.

Multiple part setups per pallet are also possible since multiple start locations can be measured and stored in the system. Electrode offsets for die-sinking EDM applications can also be obtained using this technique. Time spent on workpiece setup is done only once when the workpiece is placed on the tooling system. The cost savings is recouped every time the workpiece is moved to another machine tool using the tooling system. Since the tooling repeats to close tolerances, the zero point is automatically set each time it is clamped to the pallet of a machine table.

The use of an automation-ready tooling system lets the operator stop a job, remove it from the machine, and then return it to the machine later for completion without losing any of the setup or machining time invested in the part. This flexibility makes the shop more responsive to customer demands without sacrificing productivity.

Step Seven: Automatic Loading And Unloading
Automation systems can be applied to today’s CNC equipment. One method is a one-robot-to-one-machine approach. The machine is the master and the robot – or pallet changer – is the slave. The handling system is a self-contained unit consisting of a pallet magazine, a pallet manipulator or robot, and an integrated safety system. Shops can place these stand-alone units next to an existing machine tool to create a one-machine cell.

A program in the machine tool usually controls the system. The program has codes that call for the part to change out after the cutting cycle is finished.

Each part in the pallet-changer is loaded, machined, and returned to the magazine when finished. This continues until all of the parts are completed. The operator unloads the magazine, reloads it with new work, and sets up new programs in the machine tool for the next run.

The advantage is easy comprehension and running. Program implementation is less expensive. The disadvantages are such programs require more human intervention and lack flexibility – a workpiece is dedicated to a particular machine tool. If the machine stops due to a problem, the remaining workpieces remain incomplete

Larger multiple-machine systems can use one robot to support multiple machine tools. Workpieces are stored in a central magazine and loaded into an available machine tool. This is a large-scale system that requires a software- based cell controller to maintain and orchestrate the cell’s work movement. If a machine tool goes off-line, the work is routed to another machine in the system and it is not tied to a particular machine tool. This provides flexibility in scheduling and fault-tolerance that guarantees workpieces will be completed on time.

Step Eight: System Integration and Options
When a shop adds an automated system, integration issues improve the system’s productivity.

While a system’s hardware – such as the machine tool, the robot, and other items – are often a shop’s primary focus, some of the most important features lie in the software. The software deals with process information. Without a quality cell management system to monitor and direct the workflow, the system is rendered useless. Key software features include:
· A pallet ID system that identifies workpieces as they move around the shop floor. This system consists of a reading-head mounted on a presetting station and the robot and a set of ID chips; one chip mounted on each cell pallet. With these chips, the pallet is identified by the system as a part is loaded and then checked before the robot loads it into the machine. This prevents parts from being machined with the wrong program or tool.
· A central database that stores all of the information on work in the cell. Operators get up-to-the-minute information on job status.
· This information can also be passed to the company’s business systems to update delivery schedules, job costing, or other factors. With this information available through the company’s network, sales personnel can get the latest information about a customer’s job status.
· A user-friendly operator console for monitoring the system and performance system functions, such as adding new jobs and scheduling the order of work to be machined.

Each of these software components, combined with automation hardware, gives the company an up-to-the-minute picture of processed work.

Wrap-Up
For an automated system to function in a job shop environment the entire shop must be committed to making it work and all bottlenecks must be addressed. Another important point is to purchase new technology in quantities that can be quickly absorbed and implemented by a shop’s production environment

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