CNC Milling of Plugs and Direct-Machined Mold Tools

IBEX 2010 – Session 303September 29, 2010Doug Blount – DLBA Robotics, Ltd.JP Schroeder – ATC Formulated Polymers, Inc.

I. Introduction

•Plugs, Molds, and Limited Production Molds

•CNC Tooling Manufacturing Process•Limited Production Molds in Action•Limited Production Mold Options•Open Discussion

II. Plugs and Molds

•Plugs, Patterns, and Master Patterns•Molds and Limited Production Molds

(LPMs)•Advantages and Disadvantages•LPM Materials •Manufacturing Times•General Cost Economics

Plugs, Patterns, and Master Patterns•An exact replica of the final desired product

Production Molds (Hard Tooling)•A cavity from which a substance is shaped

(Webster’s dictionary)

Limited Production Molds (LPM)

•Mold Tooling in which only limited number of parts can be constructed

Advantages / Disadvantages of Production Molds•Advantages

▫Durable – many parts may be produced▫Provides a Quality finish

•Disadvantages▫Expensive▫Requires a long time to manufacture▫Requires a Plug or Master Pattern▫Requires a skilled labor force▫Difficult to modify

Advantages / Disadvantages of Limited Production Molds•Advantages

▫Provides a Quality finish▫Less expensive to manufacture▫Shorter lead time for the first production

part▫No Plug required

•Disadvantages▫Fewer parts produced▫Requires inside storage

LPM Materials•Tooling Boards (Tooling Board, MDF, Foams)•Tooling Pastes or Compounds

▫Polyesters (Primary focus for this presentation)▫Epoxies ▫Polyurethanes

LPM Materials: Polyester Compounds• The best cost/performance ratio• Applied with off the shelf equipment• Conventional MEKP catalyst• Application

▫Spray▫Extrude

LPM Materials: Epoxy Compounds•Higher specifications than polyester compounds•Applied with dedicated & expensive equipment•Accepts conventional finish systems•Application

▫Extrude only

LPM Materials: Urethane Compounds

• Applied with dedicated equipment• Need to manage worker exposure to uncured

material• Application

▫Extrude only

LPM Materials: Application

•Spray▫Multiple thin layers▫Longer cycle on smaller parts▫Need to manage overspray

•Extrude▫Applied in one layer▫Requires attention to prevent air entrapment▫Best for smaller parts

Relative Manufacturing Times for Production Molds•Produce the Plug (1 time unit)•Finish the Plug (0.5 time units)•Produce the Mold Tool from the Plug (1

time unit)

Relative Manufacturing Time for Limited Production Mold (LPM)•Produce the LPM (1 time unit)•Finish the LPM (0.5 time units)

General Cost Economics

•Plug ~ 1 cost unit•LPM ~ 1.25 cost units•Production Mold ~ 2.5 cost units

(including plug)

Cost Units

Number of parts being Produced

The Tooling Compound•Tooling compound is an important consideration in

your economic and quality decision▫ Accounts for approximately 20% of the overall cost▫ A significant impact on the performance of the tool!

III. CNC Tooling manufacturing Process•How does the process begin?

A Great Idea

Plug / LPM Construction Plan

•Computer Surface Model•Base Structure•Low Density Layer•Glass shell•Tooling Resin•Surface Finishing

Computer Models

•3-D Surface models of the Project▫Many formats are acceptable▫Designers can start with a sketch

Base Structure•Supports the tool during shipping and

part production•Allows the tool to be moved safely•Necessary for Dimensional Stability

Low Density Materials

•Typically Foam (Poly-Iso, Expanded PS, and Extruded PS are most common)

Fiberglass Layer• Protects the foam by distributing the load• Improves adhesion between the foam and

tooling resin• Greatly aids in the de-molding process

Tooling Compund is Applied

•Applied to the tool prior to the final machining

Final Machining

•The tool is cut to match the original model

Surface Finishing•The final Top Coat should be selected to best fit

the customer’s needs for his next step

Part Inspection and Verification•Dimensions are checked against the

specifications

Temperature•Best results are obtained when the tool is built under constant temperature and humidity• It applies to the chemistry but also to the machining•Tighter tolerances are possible in a controlled environment•The same applies to making the part from the tool!

IV. LPMs in production

•LPMs can hold vacuum for bagging and infusions

LPMs produce small and large parts

V. Options for LPM Construction•A Tooling Compound substrate can be built without low density material•For example, it can be a wood substrate•Between 10 and 20 parts can be made from such tools, even with a complex deck

LPMs Allow Changes•Should the part require a change, it is possible to do so with LPMs before

committing to hard tooling•Modular LPMs can make lengthening or widening easier

VI. Open Discussion Questions on CNC manufactured tools•Why can’t I store tools outside?•How many parts will my limited

production mold produce?•Can I use low shrink polyester tooling

systems on my CNC plug?•Can I make an epoxy part on my polyester

CNC plug or LPM?•Cracking: what to watch for•Process service temperature?

Thank You for your Time