Side Action Flash, Part 1, Mold Engineering Software

Have you ever seen a mold with the side action flashing across the split face? Have you checked the design and the steel over and over only to find that the dimensions appear to be correct? The flash problem may be due to an under-designed mold plate. This is particularly true with “A”-side action molds for large parts, and even more so when the side action is contained in a mold plate with a “through-pocket”, like the one shown below.

In this case, each part has 1.25 square inches of surface area for the cavity pressure to generate force on. This force must be overcome by the strength of the plate. Let’s assume that the cavity pressure is 10,000 p.s.i., which is not an unreasonable assumption. This is a 4-cavity mold, so the force trying to separate the slide faces is 50,000 pounds.

You have two types of plate distortion to calculate here: one is the stretching of the 2 legs that form the upper and lower boundaries (the ends) of the pocket. You can get a better visualization of that in the DZynSource Mold Engineering Software screenshot shown below. The other distortion is the “bow” of the sides of the pocket, again see the DZynSource screenshot.

You can see from the calculation here that the center of the plate, left as designed, would blow apart approximately .0012 inches, which would probably flash when molding a polypropylene part. In this case, as you can see in the drawing, the plate weakness was overcome by installing an interlock between the slide pocket plate and the stripper plate. This interlock gave the plate enough additional strength to mold flash-free parts. Of course, if the designer had the DZynSource Mold Engineering Software, this problem could have been avoided by doing “what if” scenarios with plate sizes and thicknesses to come to a more robust design that would not flash without extra mold components.

How Much Will That Round Tapered Part Stretch or Crush?

When an object of round tapered cross section is subjected to tension or compression within the elastic limit of the material, the deformation can be approximated with the equation:

¶ = FL/(p E R1 R2)

Where

¶ = = the deformation

F = the load or force

L = the length of the object in the direction that the force is acting

p = Pi (3.14159265358979)

E = the Modulus of Elasticity of the material

R1 = the radius at the small end of the cone

R2 = the radius at the large end of the cone

This equation works for tapered cylinders that don't get too small at the small end. The answers become meaningless (they approach infinity) as the radius approaches zero.

You have to use several menus to get to this form. From the Main menu, choose “Strength of Materials”; from there choose “Elastic Strain”. Once the Elastic Strain sub-menu is open, you have three choices; choose “Tapered Cross-Section, Single Material”.

When entering the required information, it is imperative that the units used are consistent. For instance, if pounds per square inch are used for the modulus of elasticity, quantities must be entered in units of pounds and inches.

First choose whether you want to use p.s.i. or N/mm²; next choose how many places beyond the decimal point you like the answer carried.

Enter the Force, the length, the large radius, the small radius, and the Modulus of Elasticity in the text boxes next to the questions asked. When entering modulus of elasticity values like 30,000,000 pounds per square inch, as would usually be used for steel, you may enter as 30e6 as a shortcut.

Press Calculate. The strain and stress values are shown on a separate Answers form. Answers are valid if the stress is from a static load and is within the elastic limit of the material in question.

Use the Clear button to clear all of the text boxes; however this is not necessary in order to do another calculation. You may simply type over the previous entries.

You may send the page to your default printer by pressing Print.

Press Menu to return to the main menu selection area.

How Many Surface Feet per Minute is That?

It is sometimes desirable to calculate the quantity of surface feet per minute attained, when the diameter of the rotating cutter (i.e. milling) or the work piece (i.e. turning) is known, and the RPM's are established. The equation used in this calculation is:

SFM = (Pi * Diameter * RPM) / 12

where, SFM = Surface Feet per Minute, RPM = revolutions per minute

You can find the Surface Feet Per Minute calculator under the "Machining Calculations" sub-menu.

Enter the diameter and revolutions per minute in the appropriate text boxes. Press Calculate. The answer appears in the Answer frame.

Use the Clear button to clear all fields, however this is not necessary in order to do another calculation. You may simply type over the previous entries.

You may send the page to your default printer by pressing Print.

Press Menu to return to the main menu selection area.

Compression in a Multi-Material Component With Uniform Cross Section

When an object is constructed with two different materials, and both have uniform cross-section, and both are subjected to the same tension or compression within the elastic limit of the material, the forces, stresses, and deformation can be predicted with the following equations:

F1 = F * (A1 * E1) / ((A1 * E1) + (A2 * E2))

F2 = F * (A2 * E2) / ((A1 * E1) + (A2 * E2))

¶ = (F1 * L) / (A1 * E1) = (F2 * L) / (A2 / E2)

Stress1 = F1 / A1

Stress2 = F2 / A2

Where

¶ = = the deformation

F = the total load or force acting on the objects

F1 = the load or force carried by object 1

F2 = the load or force carried by object 2

L = the length of the objects in the direction that the force is acting

E1 = the Modulus of Elasticity of the material for object 1

E2 = the Modulus of Elasticity of the material for object 2

A1 = The cross-sectional area of object 1, perpendicular to the force

A2 = The cross-sectional area of object 2, perpendicular to the force

It is assumed that the object is constructed in such a way that there is no slippage between objects 1 & 2.

When entering the required information into the DZynSource Mold Engineering Software, it is imperative that the units used are consistent. For instance, if pounds per square inch are used for the modulus of elasticity, quantities must be entered in units of pounds and inches.  See the previous article to see you access this calculation from within DZinSource.

First choose whether you want to use p.s.i. or N/mm², then choose how many places beyond the decimal point you like the answer carried.

Enter the Force, the length, the outer objects area, the inner objects area, and the Modulus of Elasticity for each object in the text boxes next to the questions asked. When entering modulus of elasticity values, 30,000,000, as would usually be used for steel, may be entered as 30e6 as a shortcut. The area of 10 basic shapes can be calculated by choosing Strength of Materials, Moment of Inertia from the main menu, choosing the desired shape, and entering the required information.

Press Calculate. A separate answer page appears with the values for Force 1, Force 2, the deflection, and stress induced in each component are shown. Answers are valid if the stress from a static load is within the elastic limit of the material in question.

Use the Clear button to clear all entry fields, however this is not necessary in order to do another calculation. You may simply type over the previous entries.

Press OK on the answer page to close that page.

You may send the either page to your default printer by pressing Print.

Press Menu to return to the main menu selection area.

What The Heck Is Modulus of Elasticity?

The Machinery's Handbook defines Modulus of Elasticity as follows: "Modulus of Elasticity, E, (also called Young's modulus) is the ratio of unit stress to unit strain within the proportional limit of a material in tension or compression". In general, the Modulus of Elasticity, for steel is 30,000,000 p.s.i. Some steels are as low as 28,000,000 and some as high as 34,000,000 p.s.i.

Stress equals the force or load applied divided by the area that the force is applied to, or Stress=F/A.

Strain is the deformation, elongation or compression, that the material undergoes as a result of the force being applied to it.

The shear Modulus of Elasticity, G, also known as the Modulus of Rigidity, is also the ratio of stress to strain within the proportional limit of a material, but in shear. It is usually expressed as a percentage of the Modulus of Elasticity, E, in tension. The Modulus of Elasticity in shear, G, is usually about 38% of the Modulus of Elasticity in tension, E.

Some values for Modulus of Elasticity for some common materials are as follows:

Aluminum, Alcoa QC-7 10,300,000 p.s.i., or 71,000 MPa

Brush-Wellman's Moldmax XL Beryllium Copper 17,000,000 p.s.i. or 117,000 MPa

Brush-Wellman's Protherm Beryllium Copper 20,000,000 p.s.i. or 138,000 MPa

Ampco MoldMATE 90 22,000,000 p.s.i. or 152,000 MPa

Steel 30,000,000 p.s.i. or 207,000 MPa

How To Calculate The Effective Diameter for a Toroid Type Cutter

When cutting less than full depth with a toroid shaped cutter, the effective cutting diameter is smaller than the actual diameter of the cutter, and dependent on the depth of cut and the corner radius. This effective cutting diameter is used for feed and speed calculations. A toroid shaped cutter is a flat bottom cutter with corner a radius that is less than half of the cutter diameter.

The formula used to calculate the effective cutting diameter is as follows:

Effective cutter diameter = 2 * (((R ^ 2) - ((R - Depth) ^ 2)) ^ 0.5) + (D - 2 * R)

where;

Depth = the depth of cut

D = the cutter diameter

R = the corner radii

In the DZynSource Mold Engineering Software, you enter the cutter diameter, the corner radii, and the depth of cut in the appropriate text boxes,  Press Calculate, and the answer appears above the Calculate button.

Use the Clear button to clear all fields, however this is not necessary in order to do another calculation. You may simply type over the previous entries.

You may send the page to your default printer by pressing Print.

Press Menu to return to the main menu of DZynSource Mold Engineering Software.

How To Calculate The Effective Diameter for a Ball Nose Cutter

When cutting less than full depth with a ball nose cutter, the effective cutting diameter is smaller than the actual diameter of the cutter, and dependent on the depth of cut. This effective cutting diameter is used for feed and speed calculations.

The formula used to calculate the effective cutting diameter is as follows:

Effective Diameter = 2 * (((R ^ 2) - (R - Depth of cut) ^ 2) ^ 0.5)

where,

R = The Cutter Diameter divided by 2



In DzynSource Mold Engineering Software, simply Enter the cutter diameter and the depth of cut in the appropriate text boxes.  Press Calculate.  The answer appears above the Calculate button.

Use the Clear button to clear all fields, however this is not necessary in order to do another calculation. You may simply type over the previous entries.

You may send the page to your default printer by pressing Print.

Press Menu to return to the main menu selection area.