10.1 Applying Materials & Density

10.1 Applying Materials & Density

Quick Answer: On CSWA, apply the material named on the drawing from the SOLIDWORKS Materials library (or enter the stated custom density) before you rely on Mass Properties. Mass is density × volume. Color and appearances do not set density. Wrong material, missing material, or a leftover mass override turns a perfect solid into a wrong numeric answer with no partial credit.

Mass Properties is not a cosmetic check at the end of the exam—it is how most part and many assembly items are scored. You can model every extrude, cut, pattern, and fillet correctly and still score zero if density is wrong. This section is the material half of that pipeline: get density right so the next sections’ mass, volume, surface area, and center-of-mass reads mean something.

Why material is a first-class exam skill

SOLIDWORKS stores density with the material definition. Volume comes from the solid body topology (and units). The product is mass:

mass = density × volume

If volume is correct but density is the default for “none” or the wrong alloy family, mass is scaled by the wrong constant. CSWA answer keys are built from the specified material and document unit system. Examiners do not “see” that your shape looks right; they grade the number you type or select.

Typical commercial/academic part items ask for mass in grams (MMGS) to two decimal places. Assembly items may ask combined mass after mates and modifications. In all cases the material step is non-negotiable.

How to apply a library material (exam workflow)

1. Open the part (or active component) that will be measured.
2. In the FeatureManager design tree, right-click Material (often shows as Material <not specified> or a previous name).
3. Choose Edit Material… (wording can vary slightly by version: Edit Material / Material).
4. Expand SOLIDWORKS Materials (and any custom library folders only if the problem tells you to).
5. Select the grade that matches the drawing note—for example Alloy Steel, AISI 1020, 6061 Alloy, ABS, etc.
6. Confirm density and units in the material dialog preview when available.
7. Click Apply, then Close.
8. Verify the FeatureManager now lists the material name under the part icon.

Do this early—many candidates apply material only after a failed first mass guess. Applying early also lets you spot “not specified” before the clock is tight.

Common CSWA material callouts

If two library names look similar, prefer the exact string on the drawing. Density differences between “generic” aluminum and a specific alloy are enough to push mass outside the multiple-choice band or fail a numeric key.

Density and unit systems

Document units control how density and mass display. CSWA part problems commonly use MMGS (millimeter, gram, second):

Trap: Building in IPS or leaving a template in IPS while the answer expects grams produces masses that look “reasonable” in pounds but are catastrophically wrong in grams—or the reverse. Set units before modeling (Chapter 2) and re-check Tools → Options → Document Properties → Units (or the status-bar unit display) before Mass Properties.

Library materials carry density in a defined unit system. SOLIDWORKS converts when your document units differ, but only if a real material is applied. No material means you are not on the exam density—do not assume “steel-like” defaults will match the key.

Appearance ≠ material

Candidates confuse three different controls:

Painting a part “steel gray” or applying a chrome appearance does not assign Alloy Steel density. Conversely, applying a correct material may change the default color—that is incidental. Grade mass from Material, not from what you see in shaded mode.

Custom density when the problem specifies it

Some items give an explicit density instead of (or in addition to) a library name:

• Example: “Material density = 0.0079 g/mm³” or “ρ = 2700 kg/m³”.

Workflow options:

1. Edit Material → create custom material in a personal/custom library with that density, apply it; or
2. Use the material dialog’s density field / custom material path available in your version; or
3. Only if the exam environment documents it, use Override Mass Properties density carefully (see warnings below).

Convert units if needed before typing. Example: 2700 kg/m³ = 2700 × 10⁻⁹ kg/mm³ = 2.7 × 10⁻⁶ kg/mm³, which is 0.0027 g/mm³. Typing 2700 into a g/mm³ field is a multi-order-of-magnitude error.

Never invent density. If the sheet names “6061 Aluminum,” use the library. If it only says “steel,” use the named steel grade on the sheet or the standard Alloy Steel entry the prep materials expect—do not type a remembered number from another problem.

Override Mass Properties — danger zone

Mass Properties dialogs and some property panels allow override of mass, center of mass, or related values. Overrides are for special industrial workflows (imported geometry with known mass, etc.). On CSWA they are almost always wrong:

• A checked override freezes fake mass while volume and CoM from geometry disagree.
• Practice files or prior attempts can leave overrides on if you reuse templates (avoid reusing dirty files on exam).
• If mass refuses to change after a clear geometry edit, open Mass Properties / mass override options and clear overrides so calculated values return.

Treat any “override” checkbox as a red flag unless the problem explicitly instructs you to set a known mass (rare on standard CSWA mechanical items).

Multibody parts and assemblies (preview)

• Single body part: one material on the part is usual; mass is that density × total volume of included bodies as configured.
• Multibody: materials can be assigned per body in advanced workflows; CSWA classic parts are usually single-body—if you accidentally create multibody without merging, material assignment and mass can surprise you. Prefer Merge result on bosses unless the problem requires multibody.
• Assemblies: each component keeps its own material; assembly Mass Properties sums components (Chapter 13). Applying material only to the assembly “virtual” level does not fix unassigned component parts.

FeatureManager and file hygiene checklist

Before measuring:

1. Material name visible and matches the drawing (not not specified).
2. Document units match the answer unit request (grams vs kilograms vs pounds).
3. No surprise configurations with different materials (configurations can store different materials in advanced use—stay on the active config the problem implies).
4. No mass override active.
5. After changing material, click Recalculate / re-open Mass Properties so you do not read a cached mental number from the previous material.

Worked mini-scenario

Drawing: prismatic bracket, MMGS, material 6061 Alloy, answer mass in grams to two decimals.

1. Fully define and feature the part; rebuild clean.
2. Edit Material → SOLIDWORKS Materials → Aluminum Alloys → 6061 Alloy → Apply.
3. Confirm FeatureManager shows 6061 Alloy.
4. Evaluate → Mass Properties → read Mass in grams.
5. If mass seems impossibly high/low for a small metal part, stop—re-check units and material before changing geometry.

Wrong path: apply blue appearance only → Mass Properties still not on 6061 density → pick a multiple-choice option near “default” density → zero points.

Connection to the rest of Chapter 10

• 10.2 assumes correct density and teaches reading mass, volume, and surface area, decimal precision, and the ~1% multiple-choice tolerance idea.
• 10.3 uses the same material assignment so CoM coordinates are physically meaningful relative to the origin or a custom coordinate system.

Material is a thirty-second step that protects every point you earn with modeling. Make “apply material early, verify name, clear overrides” automatic before you trust any Mass Properties digit.