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July, 2020

Using Subtractive Technology to Build Machine Tooling In-House

By Charlie Moncavage, CTO, inspire solutions A

dditive manufacturing technologies, such as 3D printers, are being used more frequently in factory applications than ever before. A

close cousin to this technology is subtractive man- ufacturing, which comes with much of the same value proposition. While additive manufacturing works by adding

material until a final object is made, subtractive manufacturing removes material from an initial ma- terial cartridge. Subtractive production is now making inroads into the smart factory, begin- ning with machine tooling. These technologies are gaining momen-

tum, because they offer lower labor costs, pro- duction batch sizes of one, free or inexpensive product complexity, distributed production, on-demand production, and more.

Subtractive production is now making inroads into the smart factory, beginning with machine tooling.

Before diving into this latest application,

it is important to use the correct terminology. Machine tooling is a device that holds a prod- uct in a machine during production. If the ma- chine tooling is flexible, it may stay in the ma- chine forever. Dedicated tooling tends to be specific for

each production batch of a specific part number and is replaced when the next batch is run. Ma- chine tooling is not a product carrier or fixture that supports a product during its journey down the production line and through each machine.

Machine Tooling on the Shop Floor Fancy technology, regardless of its makeup, is

still only a means to an end. In this case, machine tooling. Advancing the process of machine tooling can solve many problems in electronics manufac- turing factories. Most SMT defects originate from the stencil printing process, and many are related to poor

side the stencil printer. Many of today’s circuit boards are not completely flat, and for double- sided assembly, the circuit boards are further warped after the first reflow. The vacuum feature helps to flatten the PCB

by pulling it down onto the tooling. However, this method is expensive, both in time — often multi- day waits for the dedicated fixture to arrive — and in cost per fixture. The metal tooling also tends to be very heavy, resulting in cumbersome ma- chine insertion and removal. Pin support tooling is more widely used,

because it works well in general-purpose appli- cations, while providing instantaneous and flexible operation. Its drawbacks include in- ability to use vacuum, poor support between pins (especially for thin boards), print defects associated with poor maintenance (pins stick- ing) and a relatively high cost. There is also a tendency for stencils to bow

upwards toward the center, when there is no support outside of the PCB itself. This may re- sult in insufficient printed paste in the center and too much toward the edges.

A New Approach to Tooling The latest technology offers a mini CNC

Diagram of inspire solutions’ tooling production machine.

PCB support inside the printer. As PCBs get thin- ner, the problem of insufficient board support is exacerbated. Most engineers will agree that using dedicated fixtures provides the best board support. One great benefit is the use of the vacuum in-

machine that creates a mirror image of the bot- tom side of the PCB in a material optimized for the printing process. The material car- tridge has a level of flexibility that helps it to

align the many mechanical parts that must come together perfectly during squeegee travel —tooling plate, tooling, PCB, stencil, and squeegee. Each part has a certain tolerance and there is

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