Industrial Robotics: Creating the Right Specifications (part 2)

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Decoring

All castings will be transported automatically to the decoring cell using the conveyor system.

Core sand remaining inside the ports and water jackets will be removed by a high-frequency, low-amplitude, vibration decoring process, in fully-enclosed, universal decoring stations.

Four (4) such stations are required. Each station will be loaded and unloaded automatically.

Shot blasting

The existing BMD-DS shotblast machine will be modified to accommodate two 3500 heads per cycle, and will remain in its present location to shot blast all castings. After blasting, all castings will pass through a shot-emptying station to ensure minimum shot carry out.

Fine Finishing

Some parting-line flash may remain in recessed areas that the automatic grinders are not capable of removing. These areas will be processed using various small tools mounted on robots.

A series of robots with quick-change end-of-arm tools will be used to do fine metal removal on the casting surfaces. Each robotic cell will finish a complete casting, allowing the line to continue to operate (at lower capacity) if a cell is out of service. The robotic cells will be housed within a noise and emission control enclosure.

Chutes will be used to direct the metallic residue to a removal conveyor. Special devices will be used to check the condition and wear of the tools.

Compliant tools will be used to compensate for slight deviations in the shapes of cored holes.

Palletizing and Stretch Wrap

After final finishing, the castings will be palletized automatically and transported to the (relocated) existing stretch wrap machine.

Internal finishing and Inspection

Internal finishing and inspection will be accomplished manually.

Other aspects of the scope of work included the following additional sections:

Appointment of a supplier representative who would be the focal point for all communications on behalf of the team that is implementing the system

Safety and environmental specifications (ANSI, OSHA, and RIA robot safety codes)

FMEA ( Failure Mode Effects and Analysis )

Specification for operator manuals pertaining to individual pieces of equipment as well as the operation of the system and error recovery

Specifications for drawing format, and how information will be transferred between the firm and the supplier of the system

Preventive maintenance schedule and spare part requirements

Response time for support

Utility requirements (examples: power, compressed air, natural gas)

Installation requirements (foundation, ceiling height, rigging of equipment, and wiring specifications between electrical devices and electrical panels)

How the supplier will report schedule and project milestones

Installation package in terms of how the mechanical and electrical contracting services are defined. Typically the system mechanical layout is drawn in Autocad with referenced dimensions to a known datum on the shop floor. Equipment is lagged to the foundation, and wiring between panels, electrical junction boxes, and other devices is permanently installed using conduit, or other permanent wiring method.

How the supplier will validate the system prior to shipping the system to the firm. This is probably one of the most important items in the scope of work because the system is run-off at this point. This exercise is paramount in protecting the user and the supplier from unknown risks, prior to setting up a system on the shop floor. A system must never, ever, without exception be set up on the shop floor without being tested first somewhere else.

This milestone for testing prior to production run-off is to be viewed as report-card time, for it shows whether the supplier, albeit internal or external to the firm, will make a passing grade. In this particular example, the run-off requirements were as follows:

  • Finished castings had to be finished within a dimensional tolerance off 1/16 inch of the base material
  • Specified throughput had to be achieved
  • Error recovery and safety systems checked out
  • Equipment was all present per contract
  • The line operated at 98 percent uptime with no failure for twelve hours
  • Run-off on the shop floor. This validation exercise is typically similar to the previous run-off, and the pressure is pretty well off the team at this point because this milestone should simply be a repeat of the previous run-off

Specifications for shipping requirements, training, and production support if applicable. Systems are sometimes set up at time of installation and commissioning to run some fraction of the overall part types being manufactured. Users will require additional support to program additional part versions as various part styles are scheduled into production. This is where off-line programming can once again add value by reducing the overall programming time for new products, and permitting the system to be used in production without tying it up during programming of new parts. However, there will always be some level of validation or touch-up when new product is introduced into a system.

The casting finishing sequences for the two style cylinder heads are shown in Figures 2.1 and 3.1.

What was interesting on this project was that new technologies and applications of robots were used to accomplish the finishing.

This project also required an engineering study before the firm's team of personnel would agree to move forward with designing and building of the system, and new technology had to be validated. The challenges were:

How the robot itself would handle the foundry environment of dust, and heat during all seasons of the year

Could a robot be utilized to perform pre-machining processes on cast iron without damage to the robot itself, and premature wear due to the heavy forces applied to the castings to remove material

Could the robot and compliance devices, with grinding tools as an example, handle the variations in the castings and achieve a process where the casting was finished within a tolerance of 1/16 inch of the base material

Could a robot withstand the re-active forces if the robot needed to use chisel-type tools to remove gates and risers from the castings

These four criteria were all validated in an engineering study because they were unknowns, and risks to the success of the project. In hindsight, the engineering study was well worth the effort.

The pictures of the completed system in FIG. 4 through 5-6 illustrate that point.


FIG. 2 Casting Finishing Process for Head Style


FIG. 2.1 Casting Finishing Process for Head Style


FIG. 3 Description of Casting Finishing


FIG. 3.1 Casting Sequence

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FIG. 4 Robotic Cylinder Head Finishing

A pair of chiseling robots finishing Head Style # 2. The robots have protective suits over the robot cas

Robot (upside down) with high RPM and HP motor grinding surface of head style #1

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FIG. 5 Robotic Cylinder Head Finishing

Robot positioning cutting tool to remove flashing from the casting surface Material handling robot palletizing finished cylinder head style # 2 and ready for wrapping

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FIG. 6 Robotic Cylinder Head Finishing

Transport conveyor transferring castings from one operation to another. Notice the batch of one practice with head style 1 in single file behind style 2 Robotic finishing chamber

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Scope of Work Example - Robotic Press-Tending Case Study

In this example of a robot tending a press brake, the scope of work is significantly less in content than in the previous robotic finishing example. This case study is the second scope of work example because the application was simple, but the scope of work criteria follows very much the same theme as in the complex systems.

This project involved automation of an existing press brake that was approximately eight years old. The return on investment was indicated by the following criteria:

Single shift labor was eliminated and the operator was able to work on tasks that were more beneficial to the firm while the robot tended the press brake

The robot continued to work through breaks and lunch periods

The system was set up to be able to run for an unattended three hours every night after the first shift. With the extra work time, the robot was able to produce an extra 250 parts per shift

The robot out-produced the operator in an 8-hour shift by a factor of two. The extra throughput accounted for a significant amount of extra finished parts at the end of the shift

The robot was ultra-efficient when loading and unloading the press brake because a good amount of raw material could be queued up and the system left to run by itself. The firm could afford to be careless about set up time when it came to change-over of the brake to another job. The robot was always ready to remove finished blanks and load raw blanks.

A typical set-up change took approximately 15 minutes

1.0 General Overview

The firm is a job shop and OEM. The existing press brake is utilized on a single-shift basis, and forming sequences are fairly simple, with the parts being formed in a progressive, two-stage die. A family of parts is formed in the brake, varying in size, gage thickness, and base material. The average batch size run is 250 parts.

1.1 Purpose

The purpose of this Statement of Work (SOW) is to document the products and services to be delivered and the rights and responsibilities of the various parties responsible for their delivery.

Upon acceptance, any changes or modifications to this SOW must follow the Change Control Process defined in Section 4.1 of this SOW. All approved changes will become attachments to the original approved SOW, which will then form the new baseline upon which future changes will be measured.

1.2 Description of Work

The following will describe the products and service requirements:

  • Project Management
  • Mechanical Engineering
  • End of Arm Tooling
  • Safety Fencing
  • Mechanical Floor Layout
  • Conveyor Specification
  • Electrical Engineering
  • Electrical System
  • Electrical Panel
  • Integration at User site
  • Programming
  • Test and De-bug
  • System Run-off

(1) Six Axis robot with 1400 mm reach and 10 Kg payload

(1) Lot Motion Control Software

(1) Robot Base Plate

(1) Vibratory bowl feeding system with enclosure, vibratory track, and part escapement

(1) End of Arm Tooling (2) Gripper Bodies

(1) Powered outbound conveyor

(2) Safety System

(1) Press Brake Interface

(1) System Electrical Panel

System Documentation

6 x 6 Lay-in Nema 12 Wireway

5-foot Tall Safety Fencing

Details of the products and services to be offered as part of this project are provided in Section 3.0 of this SOW.

The development of this SOW was governed by the proposal design criteria established in Section 3. Should any of these criteria need to be modified, the team will need to re-evaluate the project scope for both performance and commercial impact.

2. DESIGN CRITERIA

2.1.1 Summary

The system is designed to robotically pick various styles of blanks and load-unload a two-stage die installed in an existing press brake, that will form blanks into finished products.

Manufacturing Process

Forming

Two forming operations (Stages 1 and 2 ). Parts are transferred from the first stage die to the second stage die. Parts are finished at stage two. See FIG. 7

The process accomplished by the press brake when blanks are loaded by the robot is a two stage crimping process. At stage one of this forming process, the blank is partially crimped, and the second stage of the process forms the final crimp

Sequence of Operations

(the cycle starts with parts in the brake tooling)

In one motion, the robot picks the finished blank from the second stage die and the half-finished blank from the first stage die

The half-finished blank is presented to the second-stage die, and the finished blank is dropped onto a gravity chute that transfers it to a container for finished formed blanks

Stacks of new blanks are arranged manually on an inbound powered conveyor

The blank stack presence signals the robot that blanks are ready

The robot approaches the inbound conveyor near the presented stack of blanks

The robot searches for the top of the new blank stack to find the first blank

The robot picks the first blank from the top of the stack. The search routine is required only for the first blank of a newly-introduced stack

The robot presents the raw blank to the first-stage die

The robot moves to a perch position away from the brake, and signals the brake to actuate

The robot repeats the cycle:

2.1.2 Customer Equipment

There is a 24-VDC interface between the robot control and the press brake. The position of the press brake ram is a required modification for the robot interface

The brake has a 6-foot bed, and is manually controlled by the operator through a foot pedal

Prints are not available for the brake. Footprint and elevation dimensions are required

Nominal blank size tolerance is within the loading tolerance of the tooling

The brake will position above the tooling to allow access for the robot gripper when removing and placing parts in the tools

Each die stage consists of a nest with pins that locate the blank in position for crimping

(1) Existing press brake

2.1.3 Customer Parts

Pre-formed blank

Ten part styles (aluminum, stainless, and mild steel plate), 16-gage, 14-gage, and 10-gage, different lengths and widths

Each blank style has three formed edges as presented to the robot system. The forming occurs somewhere else in the facility

Part weight is 1.5 lb. maximum

Part drawings provided (range in length 4" - 6" and width 3" - 5")

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FIG. 7 Sequence of Operations--Press Brake Forming

Step 1 first bending sequence

Existing brake Stage 1 and 2 forming Step 2 finished part Tooling Example

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3. The System Description

Key Assumptions

The press brake will be modified by the user to communicate with the robot control system

The user will supply the rigging and placement of the robot equipment at its facility.

Roles and Responsibilities

User

Modify existing equipment - press brake

Provide blanks with consistent pre-formed edges for reliable feeding of blanks to the robot system

Builder

Provide deliverables outlined in deliverable section


FIG. 8 Example of Press Tending Robotic Work-Cell

Key Requirements

15-second process cycle time per piece

System Components

(1) Robot - Six-axis robot with 1400-mm reach and 10- Kg payload - all specifications for robot listed here ( not shown )

Robot Mechanical Options

Robot Software Options:

(1) Robot Base Plate

The riser base plate is required to locate the robot at the ideal elevation for robot reach during the LUL process, as well as to secure the robot to the floor.

(1) Inbound Feeding System

Raw blanks will be randomly nested in a vibratory bowl feeder and transferred via a vibratory track to an escapement for robot picking. Unattended production is required for up to 250 blanks, which will need to be the minimum bowl capacity

Raw blanks will be loaded into the bowl manually

Blanks will be positioned consistently for robot picking at the end of the vibratory track and escapement, with the orientation required for loading the blank into the stage-one die

Blanks will exit the bowl, travel down a vibratory track, and then be positioned against a hard stop location for robot picking

The bowl feeder will require a sound enclosure to reduce noise

The robot control system will control the bowl feeder

The bowl feeder will be configured by the operator during a tool changeover in order to feed the new part style

(1) End of Arm Tooling (2) Gripper Bodies

The robot will utilize a dual vacuum gripper, capable of picking two blank styles on the top-formed surface of the blank size

The vacuum cups will be configured to pick any blank Part presence detection will be required

(1) Outbound conveyor

This conveyor will transfer finished formed blanks out of the system to a user- provided buckhorn conveyor

(1) Safety System

The safety system is responsible for preventing accidental exposure to the system. The system will utilize prefabricated steel frames with wire mesh panels, interlocked access doors, remote e-stops around the cell, operator awareness signs, and a system light tower.

(1) Press Brake Interface

24-VDC discrete I/O interface will be required between the robot and the press brake system

The position of the brake ram will be monitored by adding sensors to the brake to detect the ram fully- open or -closed position

The brake actuation will be controlled by the robot system through the existing foot pedal control of the brake system

The signals between the brake and the robot system are as follows:

Robot controller inputs (from press) -- Robot controller out-puts

Press service request -- Robot ready

Ram in position -- Press cycle start

Ram clear -- Robot clear

(1) Electrical Panel

The Electrical Panel houses the electrical hardware for the safety relays and the I/O terminations connecting the mechanisms and the robot system

Robot Programming and Test

Robot programming consists of developing the software to handle the blanks during the forming process.

The programming must teach positional points, integrate the I/O status of the independent elements, handle errors and operator requests, and provide teach-pendant operator interface information. The system will be programmed for the robot to service the single press brake. All ten part styles will be programmed. Other parts can be added and will be evaluated at the time of the firm proposal.

Demonstration at User Plant

The demonstration run-off at the user plant is designed to verify the capability of the automation system. The brake will be in its normal location on the user's shop floor, and the inbound/outbound system and robot will be set up to show the functionality of the automation system

Acceptance Criteria is running four part styles, in batches of 50 parts each

Parts will be inspected for crimping tolerances using a manual gage. The crimping tolerance is defined as f 0.75 mm, which is the tolerance now used in running the forming process manually

The demonstration at the user facility is intended for verifying the capability of the automation sys tem at the installation site. All machines and robotic equipment will be set up and run at this point.

Operation of all programming and loading will be verified.

Installation & Commissioning

Type of Installation: Guidance Installation.

Agreed-upon criteria for installation guidance will be provided

Integration and Demonstration at Customer

System integration encompasses the effort related to commissioning of the automation system on the user's floor. These efforts include supervision of the component installation, final electrical and pneumatic connections, inter-machine connections, and on-site robot programming, which will result in a system that meets the agreed-upon acceptance criteria. Additional information required to prudently address this element will be developed as required.

Training

Type of training: Operator

Number of training days: 4

Shift: First

Documentation

System documentation includes one (1) set of the following items:

  • Standard Robot Manuals (CD)
  • System Documentation (CD)

Robot cell operating instructions

Mechanical and electrical drawings for all system components

Bill of material of all components supplied

Recommended spare parts list with part numbers, name of manufacturer, and description

Paper and electronic copies of all robot programs

Safety assessment

Project Management

The Project Manager coordinates all details of the project to ensure that all needs and resources are balanced to meet the customer's schedule and delivery requirements.

Scheduling, design reviews, approvals, engineering change orders, etc. are all coordinated through the Project Manager.

Well-organized and executed to the highest level of performance. The efforts of the Engineering Team, Manufacturing, and Integration are all coordinated through the Project Manager.

The Project Manager ensures that all projects are:

Numerous examples could be included in this text to show what the scope of work would look like. Every project is different, and the purpose of this section is simply to offer a flow chart for how information can be organized. The fact that the information is required is unarguable, but how information is formatted and presented is entirely up to the engineer. The two examples certainly have different styles.

This section concludes discussion of the best practices for robot implementation. Focusing on the basics first was the theme of Sections 2 through 4 because the up-front planning process is so important in leading up to the preparation of a scope of work.

Subsequent sections will focus on the meat of robotics automation, and how it is applied.

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