Hydroform Machine Selection
Machines for the Hydroform process include both deep draw machines and fluid cell machines. aPriori selects the feasible machine of the appropriate type (deep draw or fluid cell—as specified by the machine property Machine Forming Type) with the lowest overhead rate. Overhead rate is the sum of the machine properties Direct Overhead Rate and Indirect Overhead Rate.
The appropriate machine is determined by the current routing. That is, for a deep draw routing, aPriori tries to select a deep draw machine, and for a fluid cell routing, aPriori tries to select a fluid cell machine. (The machine selection code checks for the existence of a node in the current routing with a deepDrawFormed attribute. If there is one, aPriori tries to select a deep draw machine. Otherwise, if there is a node in the current routing with a fluidCellFormed attribute, aPriori tries to select a fluid cell machine. If the current routing has no node with either attribute, machine selection fails.)
aPriori selects only from preferred machines, if there is a feasible preferred machine of the appropriate type and the cost model variable usePreferredMachines is set to true (the default in starting point VPEs). If there is no feasible preferred machine of the appropriate type, or if the cost model variable usePreferredMachines is set to false, aPriori selects from all machines. A machine is preferred if the machine property isPreferred (typically displayed as Is Preferred) is true.
See Machine Feasibility for Hydroform for more information.
Machine Feasibility for Hydroform
A machine is feasible if it can accommodate all the following part characteristics:
• Blank dimensions:
o For machines with rectangular tables, blank length and width (including any addendum) must be less than the machine properties Forming Area Length and Forming Area Width, respectively.
o For machines with circular tables, blank diagonal length (the square root of the sum of the squares of the blank length and width) must be less than the machine property Forming Area Dia.
• Forming depth: part height must be less than the machine property Max Draw Depth.
• Required forming pressure: the required forming pressure must be less than the machine property Max Pressure.
Required pressure depends on the following
o Material yield strength
o Part’s smallest bend radius
o Blank thickness.
• Required punch force (deep draw machines only): for deep draw machines, the required punch force must be less than the machine property Lower Punch Force.
Required punch force depends on the following:
o Blank thickness
o Material yield strength
o Blank width (including any addendum)
o Aggregate width of primary forms
Required Forming Pressure for Hydroform
The forming pressure required for a given part is calculated as described below.
Required Pot Pressure = 1.2 * Material Yield Strength *
(Blank Thickness / (Min Bend Radius + (Blank Thickness / 2)))
Required forming pressure depends on the following:
• Material yield strength: the value of the material property Tensile Yield Strength.
• Blank thickness
• Min Bend Radius: the minimum bend radius of any bend or form on the part (or, if there are no bends or forms, the minimum bend radius of any surface on the part).
The constant 1.2 is a safety factor used to ensure that the required pressure is achieved.
Required Punch Force for Hydroform
The punch force required for a given part is calculated as described below.
Required Punch Force = * Blank Thickness * Material Yield Strength *
((Blank Width / Punch Width) * 0.7)
Required punch force depends on the following:
• Blank thickness
• Material yield strength: the value of the material property Tensile Yield Strength.
• Blank width: width of the blank, including any addendum (see Width of Addendum Added to Blank Size for coil stock or Addendum Added to Blank Size for sheet stock).
• Punch width: the aggregate width of all the part’s primary forms (or the part width if there are no primary forms). See Important Forms for Hydroforming for more information.
Important Forms for Hydroforming
The Required Punch Force for Hydroform and Number of Forming Draws for a part depend on the aggregate width of the part’s important forms.
All of the following are considered important forms:
• Forms adjacent to the main surface (that is, forms that bear the LIES NEAR relation to the main surface, with a distance property of 0)
• The part’s primary form (see below)
• Other EMBOSS forms that intersect the primary form
• Downward CURVED_BEND forms that intersect the primary form
A part’s primary form is the largest-area form for which all the following hold:
• Form’s Sub Type is EMBOSS.
• Form is not on the main surface. (That is, it does not bear the LIES ON relation to the main surface.)
• Form is adjacent to the main surface. (That is, it bears the LIES NEAR relation to the main surface, with a distance property of 0.)
• Form depth exceeds blank thickness by a factor greater than the factor looked up by material type in the lookup table tblMaterialThicknessFactor.