*Note: This document is intended to highlight design and manufacturing guidelines and capabilities in order to illustrate what the company can produce. This is not an all encompassing document! Please contact ebm-papst Industries, Inc. for further information: (860.674.1515 or sales@us.ebmpapst.com )

Contents

1. Design Standards
2. CAD capabilities
3. Tolerances
4. Materials
5. Plating and Finishing
6. Tooling
7. Fabrication
8. Assembly
9. First Article Inspections

1. Design Standards

All inner radii on sheetmetal designs are formed using metric sizes. 1mm inner bend radii are, by far, the most common size. As material gets thicker and softer, larger bend radii must be used. We require 2mm and 3mm radius tooling for aluminum thicker than 18 gage, (.040), to prevent cracking. We have a large stock of 1mm bend tools, but a smaller selection of 2mm and 3mm tools. There may be a lead time associated with certain 2 and 3mm bend tools.

Large, punched grill-style openings, (finger guards), are difficult to keep flat. Specifically, openings greater than 6” distorts the metal such that the resulting “oil-canning” can make it impossible to reliably control the height of the surface to within .030”. Design alternatives include screw-on wire guards and spot-welded perforated metal sheet.

In thin material such as 18 and 20 gage material, countersinking screws should be avoided if possible. There is not enough material thickness to accept the height of the screw head such that the head of the screw will be flush with the fastened surface. Rivets can be made flush, even in thin material, and should be considered. (ebm-papst is working with PEM engineers to develop a custom PEM nut design that will remove this limitation, but until this is available, avoid the countersunk screws if possible.)

Any cut-out feature, (holes, rectangles, obrounds), will have distorted edges if those edges are placed too close to a bend. A recommended distance for cut-outs is 4 times the material thickness away from a bend.

A pressed inserted component, such as a stand-off or a PEM nut, needs to be a certain distance away from a bend to allow clearance for the insertion tool. Typically the minimum distance from a stand-off centerline to a bend is ½”, and .290” is the minimum distance for a nut.

The silk-screening process for labels is typically done after forming. It is therefore important to allow silkscreens to be located on the outside of a box rather than the inside. As an alternative, many customers are switching to overlays (labels) as silk-screening is an expensive, “art” work center.

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2. CAD Capabilities

We use Pro/Engineer version 2001 as our primary CAD software. All modeling in Pro/Engineer is performed in a sheetmetal-specific, solids-based environment using integrated functionality for flat pattern generation. We can read any version of Pro/Engineer files. For greatest efficiency, the customer should model their products in the sheetmetal environment, and should design using the 1mm bend radius standard.

Ideally, ebm-papst will receive CAD files in Pro/Engineer, which we consider our native CAD format. Models received in Pro/Engineer format will be used directly, and will typically require little to no remodeling. In addition, we are able to convert any of the 3D neutral file formats, such as IGES, STEP, ACIS SAT, Parasolid X_T, directly into a 3D model. Formats such as DXF, DWG, .pdf, are almost exclusively a 2D representation, and would need to be completely modeled from scratch.

In addition, we have a seat of both SolidWorks 2001 and SolidEdge version 9. We can receive native files from these systems and convert the files into Cadkey or Pro/Engineer.

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3. Tolerances

Tolerances must be assigned to components with consideration as to what is reasonable, what is practical, and what the manufacturing machines are capable of producing. We should keep in mind, when discussing capabilities, that our equipment is new, state-of-the-art equipment, and our shop floor leaders have been involved with sheetmetal manufacturing for many years. The manufacturing tolerances that we can achieve are as good as any other state-of-the-art sheetmetal manufacturer.

Single-punch hole size tolerances are largely a function of the punch and die used to create them. In general, there is very little variation from one hole to the next. We are able to achieve a tolerance of +/-.003” on holes. We can hold +.003/-.000” on holes which require a pressed component, such as a PEM nut. Keep in mind that the diameter is what will pass through the hole, and not the “rim size”, which may be slightly different.

Hole to Hole / Hole to Edge tolerances are controlled by the CNC Punch Presses, and are therefore executed during the flat pattern stage. We expect to hold flat pattern geometry to +/-.010”. Although the punch presses can at times hold up to +/-.004”, flexing in the material, and distortion due to the amount of holes on a surface make tight tolerances unreliable.

Hole to Fold / Fold to Fold tolerances are controlled during the bending stage on the Press Brakes. Although our press brakes can repeat to .001”, the error is greatly compounded by variations in material thickness (as much as +/-.007”), and the variation in the flat pattern, (+/-.010”). We can meet a tolerance of +/-.020” on bends. A tolerance of +/-.010” can be held, but should only be specified when absolutely necessary.

Keep in mind that exceedingly tight tolerances force additional labor in sorting and inspection. The result of tolerances that are too tight is simply higher costs and lower productivity. Correctly toleranced parts still have excellent fit and function, with the added benefit of efficiency.

If extremely tight tolerances are truly required, (ie. +/-.005” or less), and the tolerances exceed the capabilities of our manufacturing machines, then we are forced to consider dedicated tooling and custom processes.

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4. Materials

The cold rolled steel, (CRS), that ebm-papst uses is ASTM-A366, which contains a carbon content of .10 and a temper of #2 or #3, which improves welding and forming. Steel is much easier to spot weld than aluminum. It is also much cheaper, although adding corrosion protection, (plating and painting), may consume much of the cost savings. Thickness can vary as much as +/-.007”.

The aluminum that ebm-papst uses is 5052-H32, it has has been strain hardened and stabilized by low temperature heating and is 1/4 hard. Its main alloy is magnesium. 5052-H32 is a very strong aluminum, yet can be formed with a reasonable bend radius. All aluminum will crack along a bend if a tight bend radius is used. An inner bend radius of 1 to 1 ½ material thickness minimum is required. Corrosion and weldability of 5052-H32 is considered very good.

In cases where aluminum is being substituted for steel, the material thickness will need to be approximately 40% thicker in aluminum to have the same strength. However, since aluminum is 1/3 the weight, the aluminum version of the sheetmetal will still be ½ the weight of a steel version.

The stainless steel that ebm-papst uses is 304. It is the most widely used of the stainless steel and heat resisting steels. It offers good corrosion resistance to many chemical corrodents as well as industrial atmospheres. It has very good formability and can be readily welded by all common methods.

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5. Plating and Finishes

Steel is often purchased with a galvanized coating to prevent rusting. It is important to remember that certain plated materials such as Aluminized Steel can’t be safely TIG welded.

Plating that is applied after forming and welding is done by an external supplier.

Standard powder-coat paint is applied in-house. Designers are required to compensate for the material build-up, and typically use .005” thickness per surface as a rule. This is usually the reason why ebm-papst’s drawings have dimensions that are .010” less than what the customer has specified. Excessive masking of surfaces is expensive and labor intensive. Powder Paint with a substrate of Zinc Chromate is not recommended because out gassing will cause pitting of the paint surface.

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6. Tooling

The punch press department has a large inventory of tools for round and rectangular cut-outs. For formed features, there is an inventory of tools that were ordered for specific jobs. On new jobs that require form tooling, if a special tool has to be ordered, there typically is a 4-6 week lead time. The maximum offset height of a formed feature is 3/8”.

For hex pattern finger guard cutouts, we have currently have tooling for 5/32” x .035 web, ¼” x .040/.048” web, 5/16” x .060” web, 3/8” x .060 web, ½” x .06 web. Other sizes may have to be ordered.

If possible, avoid selecting an air mover that is on the edge of the CFM requirement, so that special finger guards or punch patterns are required.

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7. Fabrication

We prefer spot welding over TIG welding if there is a clear functional choice. It reduces labor content and tends to be more repeatable. We like to avoid fillet welding to cosmetically seal box corners. We have an alternative design for “tab through and TIG weld construction” which avoids the cosmetic grinding after weld.

POP rivets and screws become the only options to fasten together two components that have been plated. In general, POP rivets are cheaper than screws, and the labor content is less, but rivet construction makes the unit much less servicable.

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8. Assembly

Through bolting fans to the sheet metal housing with a blind PEM stand off is the most common way of fastening the fans to the chassis. Using pressed or thermal inserts in the fans should be last resort, as well as loose nuts and bolts.

Fan tolerance stack up is critical, especially when dealing with impellers. Typical clearance between impellers and inlet rings is between .060” and .090”. Thought needs to be put into lead exit and routing so that it does not rub when space is limited.

We typically use in-line torque fastening equipment. Place fasteners perpendicular to the work surface if possible.

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9. First Article Inspections

A First Article Inspection will be performed on at least one unit for all prototype builds. No product will be released to production without a satisfactory First Article Inspection. The Quality Department is responsible to perform dimensional, component and workmanship inspection in accordance with customer drawings and specifications. In cases where the customer hasn’t provided ebm-papst with drawings that detail critical dimensions, then ebm-papst must provide the customer with an inspection drawing, which the customer must approve.

If a unit fails First Article Inspection, a manager may release the unit for shipment upon notification to and approval by the customer. A failed First Article Inspection triggers a review meeting in which a determination is made as to the cause of failure, and corrective action is taken.

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