Material Stock and Utilization

The Stock Machining process group allows you to edit and view values for:

Stock Machining Material Composition

Material composition details include:

  • Material

  • Description

  • Mode

  • Material Type Name

  • CMC Cut Code (using the Sandvik-Coromant Material Classification system)

  • Cost Per Mass ($/kg)

  • Density (kg/m3)

  • Shear Strength (MPa)

  • Hardness

  • Hardness System

  • Milling Speed

  • Turning Speed

Stock Machining Material Stock Type

Material stock types include:

  • Round Bar

  • Rectangular Bar

  • Plate

  • Square Bar

  • Round Tube

Material stock details include:

  • Stock Name

  • Description

  • Stock Form (Round Bar, Rectangular Bar, Plate, Square Bar, or Round Tube)

  • Stock Dimensions (dependent on stock form, e.g. Length (mm), Width (mm), Thickness (mm), Outer Diameter (mm), Inner Diameter

  • Cost Per Mass ($/kg)

  • Hardness

  • Hardness System

Material Stock Alignment and Cross-section Determination

When costing a part, aPriori automatically determines the most likely stock form and alignment direction. To do this, it analyzes the geometry of the part and evaluates potential stock axis directions and cross-sections from these directions. To view the chosen stock cross section, click the Stock Form and Alignment button in the Component Viewer tool bar.

To choose a different stock form or align the stock differently, use the Stock Form and Alignment tool in the Component Viewer. For more information, see the "Defining stock form and alignment for the Stock Machining and Bar &Tube process groups" section of the aPriori Professional User Guide.

Note: Changing material stock form and alignment may affect material utilization.

Round parts are generally assigned a round cross-section (allowing the selection of round stock). But for parts that are, roughly speaking, flat and round, geometry extraction assigns a rectangular cross-section (and may select plate stock). Parts are considered flat and round, in this sense, if both the following hold:

  • Part’s round cross-section diameter is greater than or equal to the value of the site variable maxRoundStockDiameterMm (304.8mm in starting points).

  • Ratio of part thickness to round cross-section diameter is less than or equal to the value of the site variable maxRoundStockAspectRatio (0.2 in starting points).

If either of these site variables is -1, aPriori may select the round cross-section rather than the rectangular one.

In starting point Digital Factories, plate stock is auto-selected by aPriori only if the part width is greater than 142.4mm and the height-to-width ratio is less than 0.25. Digital Factory Administrators can customize these thresholds with the cost model variables minPlateTriggerWidth and maxPlateTriggerHeightOverWidth.

Stock Machining Material Stock Sizes and Allowances

aPriori Supports the concept of a machining stock allowance when determining the initial stock size required to machine a given part. A stock allowance typically is a small amount of extra material added to the finished part dimensions to accommodate any machining (material removal) needed to meet material quality, tolerance or surface finish requirements. A non-zero stock allowance is necessary to drive rough- and finish- machining of the part. A zero-value stock allowance means that the “as-supplied” stock surfaces are sufficient for the finished part, with no additional machining required to achieve desired quality, tolerances or surface finish requirements.

aPriori generally computes the ideal stock size required for a part based on the following:

  • Dimensions of the finished part

  • Amount of material required to meet any specified stock allowances

For non-hex stock, by default in starting point Digital Factories, aPriori selects actual stock with the smallest standard thickness greater than or equal to the ideal thickness (and only selects virtual stock if there is no such actual stock). The setup option Stock Unit System determines whether aPriori uses metric standard stock heights or US standard stock heights. See Snap Up to a Standard Stock Height for more information.

The following cost model variables determine many of the default stock allowances:

  • maxStockAllowance: default stock allowances are bounded above by this value.

  • minStockAllowance: default stock allownaces are bounded below by this value.

  • percentStockAllowance:

    • For rectangular bar, square bar, and plate stock, this percentage of the part cross-section’s height is the default height allowance.

    • For round bar and round tube stock, this percentage of the part cross-seciton’s outside diameter is the default height allowance.

See also Stock Machining and Hex Stock and Roughing Technique for Plate Stock.

aPriori also provides process setup options to enable you to override the default stock dimensions and allowance values--see Material Stock Setup Options for Stock Machining for more information.

Stock Machining and Hex Stock

aPriori selects Hex Bar stock for a finished part with a generally hexagonal cross-section (even if the cross-section has rounded or chamfered corners). By default, Hex Bar stock has the same width (as measured across the flats of the hex) as the finished part. That is, aPriori assumes, by default, that hex features are designed to standard hex stock sizes and that those raw stock surfaces are left intact. In contrast, for round and rectangular bar stock, aPriori chooses a standard stock size that provides a non-zero stock allowance, so that all raw stock surfaces are machined away to produce the finished part. 

For Hex Bar parts that are machined down from a larger stock, use the process setup option Stock Width Across the Flats Dimension to specify either a stock allowance or the absolute hex stock size. Administrators can change the default stock allowance for Hex Bar (0 in starting point Digital Factories) with the cost model variable hexMinStockWidthAllowance or the cost model variable hexPercentStockAllowance.

The following site variables constrain when Hex Bar stock is chosen:

  • maxHexWidthAcrossFlats: Hex Bar stock is chosen only if the width (as measured across the flats) does not exceed this value (101.60mm by default).

  • preferRoundStockforHexProfiles: this is false, by default. If set to true, Round Bar or Round Tube stock, rather than Hex Bar stock, is chosen for parts whose largest external cross-section profile is hexagonal.

Regardless of these site variable settings, you can use the Stock Form and Alignment dialog to specify the desired stock form for a part with external hexagonal features.

Stock Machining Material Utilization

For non-plate stock, material utilization options include:

  • Computed — aPriori computes the utilization based on comparing the finished size of the part to the size of the starting material stock.

  • Machine Default — aPriori uses the selected machine’s default utilization value.

  • Override — aPriori calculates initial material mass and cost by dividing part finished mass by a user-entered utilization rate.

For more information on selecting the machining material utilization mode, see Manufacturing Process Information > Selecting material > Change material utilization in the aPriori Professional User Guide.

See also Roughing Technique for Plate Stock.

Stock Machining Routing and Plate Stock

When plate stock is selected for stock machining, Bulk Milling is assigned to the part if both the setup option Roughing Technique for Plate Stock is set to All Bulk Milling.

When plate stock is selected for stock machining, perimeter cutting is assigned to the part if both the following hold:

Perimeter cutting appears in two nodes in the Manufacturing Process pane:

  • Perimeter Cutting (under the Stock Machining node): by default, the Perimeter GCD is assigned to Waterjet Cutting from the Waterjet Cut process in the Sheet Metal process group; Plasma Cut, Oxyfuel Cut, and Laser Cut (also from the Sheet Metal process group) are available for manual selection. See Sheet Metal - Soft Tooled.

    Note: In the Stock Machining process group, the nesting layout is controlled only by process setup options accessed via the Material Stock process.  However, if you are using the “Plate Cutting with Dropoff” routing technique, a 2D sheet metal cutting process (such as Water Jet or Laser) will be assigned for cutting the part perimeter from the plate.  That sheet metal process also provides process setup options related to nesting, but these options will have no effect when costing the part in the Stock Machining process group.  They are used for controlling nesting layouts when costing parts inside the Sheet Metal process group.

  • Perimeter Cut (under the Machining node): this process applies the operation As Perimeter Cut to the perimeter’s surfaces.

When plate stock is selected for stock machining, the Perimeter Milling Operation operation is assigned to the Perimeter GCD if both the following hold:

Bulk milling is also available; see Roughing Technique for Plate Stock.